Protective coating for separators for electrochemical cells

ABSTRACT

This invention pertains to separators for use in electrochemical cells which comprise at least one microporous pseudo-boehmite layer, which separator is in contact with at least one protective coating layer positioned on the anode-facing side of the separator opposite from the cathode active layer in the cell; electrolyte elements comprising such separators; electrical current producing cells comprising such separators; and methods of making such separators, electrolyte elements and cells.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/399,967, filed Sep. 21, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 09/215,029,filed Dec. 17, 1998, the contents of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

[0002] The present invention relates generally to the field ofseparators for electrochemical cells. More particularly, this inventionpertains to separators for electrochemical cells which comprise at leastone microporous pseudo-boehmite layer and at least one protectivecoating layer; electrolyte elements comprising such separators; electriccurrent producing cells comprising such separators; and methods ofmaking such separators, electrolyte elements, and cells.

BACKGROUND

[0003] Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent specifications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

[0004] In an electric current producing cell or battery, discharge ofthe cell from its charged state occurs by allowing electrons to flowfrom the anode to the cathode through an external circuit resulting inthe electrochemical reduction of the cathode active material at thecathode and the electrochemical oxidation of the anode active materialat the anode. Under undesirable conditions, electrons may flowinternally from the anode to the cathode, as would occur in a shortcircuit. To prevent this undesirable internal flow of electrons thatoccurs in a short circuit, an electrolyte element is interposed betweenthe cathode and the anode. This electrolyte element must beelectronically non-conductive to prevent the short circuiting, but mustpermit the transport of positive ions between the anode and the cathodeduring cell discharge, and in the case of a rechargeable cell, duringrecharge. The electrolyte element should also be stableelectrochemically and chemically towards both the anode and the cathode.

[0005] Typically, the electrolyte element contains a porous material,referred to as a separator since it separates or insulates the anode andthe cathode from each other, and an aqueous or non-aqueous electrolytein the pores of the separator. The aqueous or non-aqueous electrolytetypically comprises ionic electrolyte salts and electrolyte solvents,and optionally, other materials such as for example, polymers. A varietyof materials have been used for the porous layer or separator of theelectrolyte element in electric current producing cells. These porousseparator materials include polyolefins such as polyethylenes andpolypropylenes, glass fiber filter papers, and ceramic materials.Usually these separator materials are supplied as porous free standingfilms which are interleaved with the anodes and the cathodes in thefabrication of electric current producing cells. Alternatively, theporous separator layer can be applied directly to one of the electrodes,for example, as described in U.S. Pat. No. 5,194,341 to Bagley et al.

[0006] Porous separator materials have been fabricated by a variety ofprocesses including, for example, stretching combined with specialheating and cooling of plastic films, extraction of a solubleplasticizer or filler from plastic films, and plasma oxidation. Themethods for making conventional free standing separators typicallyinvolve extrusion of melted polymeric materials either followed by apost-heating and stretching or drawing process or followed by a solventextraction process to provide the porosity throughout the separatorlayer. U.S. Pat. No. 5,326,391 to Anderson et al. and referencestherein, describe the fabrication of free standing porous materialsbased on extraction of a soluble plasticizer from pigmented plasticfilms. U.S. Pat. No. 5,418,091 to Gozdz et al. and references therein,describe forming electrolyte layers by extracting a soluble plasticizerfrom a fluorinated polymer matrix either as a coated component of amultilayer battery structure or as an individual separator film. U.S.Pat. No. 5,194,341 to Bagley et al. describes an electrolyte elementwith a microporous silica layer and an organic electrolyte. The silicalayer was the product of the plasma oxidation of a siloxane polymer.

[0007] These manufacturing methods for free standing separators arecomplex and expensive and are not effective either in providingultrafine pores of less than 1 micron in diameter or in providingseparator thicknesses of less than 15 microns. The methods for making aseparator coated directly on another layer of the cell typically involvea solvent extraction process after coating to provide the porositythroughout the separator layer. As with the free standing separators,this solvent extraction process is complex, expensive, and not effectivein providing ultrafine pores of less than 1 micron in diameter.

[0008] Carlson et al. in U.S. patent application Ser. No. 08/995,089 tothe common assignee, describe separators for use in electrochemicalcells which comprise a microporous pseudo-boehmite layer and electrolyteelements comprising such separators. The pseudo-boehmite separators andmethods of making such separators are described for both free standingseparators and as a separator layer coated on an electrode.

[0009] As the non-aqueous electrolyte in the pores of the separator ofan electrolyte element, a liquid organic electrolyte comprising organicsolvents and ionic salts is typically used. Alternatively, a gel orsolid polymer electrolyte containing polymers and ionic salts, andoptionally organic solvents, might be utilized instead of the liquidorganic electrolyte. For example, U.S. Pat. Nos. 5,597,659 and 5,691,005to Morigaki et al. describe a separator matrix formed of a microporouspolyolefin membrane impregnated in its pores with an ionic conductivegel electrolyte.

[0010] In addition to being porous and being chemically stable to theother materials of the electric current producing cell, the separatorshould be flexible, thin, economical in cost, and have good mechanicalstrength. These properties are particularly important when the cell isspirally wound or is folded to increase the surface area of theelectrodes and thereby improve the capacity and high rate capability ofthe cell. Typically, free standing separators have been 25 microns (μm)or greater in thickness. As batteries have continued to evolve to highervolumetric capacities and smaller lightweight structures, there is aneed for separators that are 15 microns or less in thickness with asubstantial increase in the area of the separator in each battery.Reducing the thickness from 25 microns to 15 microns or less greatlyincreases the challenge of providing porosity and good mechanicalstrength while not sacrificing the protection against short circuits ornot significantly increasing the total cost of the separator in eachbattery.

[0011] This protection against short circuits is particularly criticalin the case of secondary or rechargeable batteries with lithium as theanode active material. During the charging process of the battery,dendrites can form on the surface of the lithium anode and can grow withcontinued charging. A key feature of the separator in the electrolyteelement of lithium rechargeable batteries is that it have a small porestructure, such as 10 microns or less in pore diameter, and sufficientmechanical strength to prevent the lithium dendrites from contacting thecathode and causing a short circuit with perhaps a large increase in thetemperature of the battery leading to an unsafe explosive condition.

[0012] Another highly desirable feature of the separator in theelectrolyte element is that it is readily wetted by the electrolytewhich provides the ionic conductivity. When the separator material is apolyolefinic material, which has nonpolar surface properties, theelectrolytes (which typically have highly polar properties) often poorlywet the separator material. This results in low capacities in thebattery due to the nonuniform distribution of the electrolyte in theelectrolyte element.

[0013] Further it would be highly advantageous to be able to preparefree standing separators by a relatively simple process of coating whichdirectly provides ultrafine pores as small as 1 nm in diameter and canreadily provide a range of thicknesses from 50 microns or greater downto 1 micron. Also, it would be advantageous to be able to prepareseparators with ultrafine pores and a wide range of thicknesses coateddirectly on another layer of the electric current producing cell by aprocess of coating without requiring any subsequent solvent extractionor other complex process which is costly, difficult to control, and noteffective in providing ultrafine pores.

[0014] A separator, particularly one with a thickness less than 25microns, which is applicable for electric current producing cells, andwhich can avoid the foregoing problems often encountered with the use ofpolyolefinic and other conventional porous materials made usingextrusion, extraction, or other processes would be of great value to thebattery industry.

SUMMARY OF THE INVENTION

[0015] The present invention pertains to a separator for use in anelectric current producing cell, wherein the separator comprises (i) atleast one microporous pseudo-boehmite layer in contact with (ii) atleast one protective coating layer. In one embodiment, the protectivecoating layer is adjacent to one outer surface of the microporouspseudo-boehmite layer. In one embodiment, the protective coating layeris an intermediate layer between two microporous pseudo-boehmite layers,wherein the compositions of the microporous pseudo-boehmite layers maybe the same or different. In one embodiment, the protective coatinglayer is an intermediate layer between two microporous pseudo-boehmitelayers, and the separator further comprises an additional protectivecoating layer on the outside surface of one or both microporouspseudo-boehmite layers, and further wherein the compositions of the twomicroporous pseudo-boehmite layers may be the same or different, and thecompositions of the two or more protective coating layers may be thesame or different. In one embodiment, the microporous pseudo-boehmitelayer is an intermediate layer between two protective coating layers,wherein the compositions of the protective coating layers may be thesame or different.

[0016] In one embodiment, the at least one protective coating layercomprises a polymer. In one embodiment, the protective coating layercomprising a polymer is a single ion conducting layer. In one embodimentof the invention, the protective coating layer comprising a polymercomprises one or more moieties from the polymerization of one or moremonomers or macromonomers selected from the group consisting of:acrylates, methacrylates, olefins, epoxides, vinyl alcohols, vinylethers, and urethanes. In one embodiment, the olefinic monomer isselected from the group consisting of: ethylene, propylene, butene,pentene, hexene, octene, and styrene. In one embodiment, the acrylatemonomer or macromonomer is selected from the group consisting ofpolyethylene glycol diacrylates, polypropylene glycol diacrylates,ethoxylated neopentyl glycol diacrylates, ethoxylated bisphenol Adiacrylates, ethoxylated aliphatic urethane acrylates, ethoxylatedalkylphenol acrylates, and alkylacrylates.

[0017] In another embodiment, the polymer of the protective coatinglayer comprises one or more moieties formed by polymerization of one ormore monomers or macromonomers selected from the group consisting ofmonomers and macromonomers having the formula:

R¹(R²O)_(n)-R³

[0018] wherein:

[0019] R¹ is the same or different at each occurrence and is selectedfrom the group consisting of

[0020] CH₂═CH(C═O)—O—,

[0021] CH₂═C(CH₃)(C═O)O—,

[0022] CH₂═CH—,

[0023] CH₂=CH—O—;

[0024] R² is the same or different at each occurrence and is selectedfrom the group consisting of

[0025] —CH₂—CH₂—,

[0026] —CH(CH₃)—CH₂—,

[0027] —CH₂—CH₂—CH₂—,

[0028] —CH(C₂H₅)—CH₂—,

[0029] —CH₂—CH₂—CH₂—CH₂—;

[0030] R³ is the same or different at each occurrence and is selectedfrom the group consisting of

[0031] cyano, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl,2-ethylhexyl, decyl, dodecyl, phenyl, butylphenyl, octylphenyl,nonylphenyl, R¹, —X—(OR²)_(m)—R¹, —Y[(OR²)_(o)—R¹]₂, —Z[(OR²)_(p)—R¹]₃;

[0032] X is a divalent radical selected from the group consisting of:

[0033] Y is a trivalent radical selected from the group consisting of

[0034] Z is a tetravalent radical selected from the group consisting of

[0035] m is an integer ranging from 0 to 100;

[0036] n is an integer ranging from 0 to 100;

[0037] o is an integer ranging from 0 to 100; and,

[0038] p is an integer ranging from 0 to 100.

[0039] In one embodiment, the polymer of the protective coating layer isselected from the group consisting of polyacrylates, polymethacrylates,polyolefins, polyurethanes, polyvinyl ethers, polyvinyl pyrrolidones,acrylonitrile-butadiene rubber, styrene-butadiene rubber,acrylonitrile-butadiene-styrene, sulfonatedstyrene/ethylene-butylene/styrene triblock polymers, and mixturesthereof.

[0040] In a preferred embodiment, the polymer has a molecular weight ofgreater than 10,000. In a more preferred embodiment, the polymer has amolecular weight greater than 50,000.

[0041] Another aspect of the invention pertains to a separator for usein an electric current producing cell, wherein the cell comprises acathode having a cathode active layer, an anode, and an electrolyteelement interposed between the cathode and the anode, and theelectrolyte element comprises a separator and an electrolyte; whereinthe separator comprises at least one microporous pseudo-boehmite layerand wherein, on the side of the separator opposite from the cathode ofthe cell, is coated at least one protective coating layer. In oneembodiment, the separator comprises a first and a second protectivecoating layer, wherein the first protective coating layer is in contactwith the microporous pseudo-boehmite layer on the side of the separatoropposite from the cathode active layer, and the second protectivecoating layer is in contact with the first protective coating layer onthe side opposite from the pseudo-boehmite layer, and wherein the twoprotective layers may be the same or different.

[0042] In one embodiment of the invention, the protective coating layercomprises a single ion conductive layer. In one embodiment, theprotective coating layer comprises a single ion conducting glassconductive to lithium ions. In one embodiment, the single ion conductingglass is selected from the group consisting of lithium silicates,lithium borates, lithium aluminates, lithium phosphates, lithiumphosphorus oxynitrides, lithium titanium oxides, lithium lanthanumoxides, lithium silicosulfides, lithium borosulfides, lithiumaluminosulfides, lithium germanosulfides, and lithium phosphosulfides.

[0043] In one embodiment, the protective coating layer comprises aconductive polymer selected from the group consisting ofpoly(p-phenylene), polyacetylene, poly(phenylenevinylene), polyazulene,poly(perinaphthalene), polyacenes, and poly(naphthalene-2,6-diyl).

[0044] In one embodiment, the protective coating layer has a thicknessof from about 0.2 microns to about 20 microns. In a preferredembodiment, the protective coating layer has a thickness of from about0.5 microns to about 15 microns. In a more preferred embodiment, theprotective coating layer has a thickness of from about 0.5 microns toabout 10 microns. In a most preferred embodiment, the protective coatinglayer has a thickness of from about 0.5 microns to about 5 microns.

[0045] In one embodiment of the invention, in which the protectivecoating layer comprises a single ion conducting glass or a conductivepolymer, the protective coating layer has a thickness of from about 5 nmto about 5 microns.

[0046] In one embodiment of the present invention, the protectivecoating layer further comprises a pigment. In one embodiment, thepigment of the protective coating layer is selected from the groupconsisting of colloidal silicas, amorphous silicas, surface treatedsilicas, colloidal aluminas, amorphous aluminas, conductive carbons,graphites, tin oxides, titanium oxides and polyethylene beads.

[0047] In one embodiment, the polymer and the pigment are present in theprotective coating layer at a weight ratio of from about 1:10 to about10:1. In a preferred embodiment, the polymer and the pigment are presentin the protective coating layer at a weight ratio of from about 1:4 toabout 6:1. In a more preferred embodiment, the polymer and the pigmentare present in the protective coating layer at a weight ratio of fromabout 1:3 to about 4:1.

[0048] In one embodiment, the pigment of the protective coating layerhas a particle size of from about 1 nm to about 10,000 nm. In apreferred embodiment, the pigment of the protective coating layer has aparticle size of from about 2 nm to about 6,000 nm. In a more preferredembodiment, the pigment of the protective coating layer has a particlesize of from about 5 nm to about 3,000 nm.

[0049] In another embodiment, the pigment of the protective coatinglayer has a particle size and the microporous pseudo-boehmite layer hasan average pore diameter which is smaller than said particle size.

[0050] In one embodiment of the present invention, the pseudo-boehmitelayer has a pore volume from 0.02 to 2.0 cm³/g. In a preferredembodiment, the pseudo-boehmite layer has a pore volume from 0.3 to 1.0cm³/g. In a more preferred embodiment, the pseudo-boehmite layer has apore volume from 0.4 to 0.7 cm³/g.

[0051] In one embodiment, the pseudo-boehmite layer of the separator hasan average pore diameter from 1 to 300 nm. In a preferred embodiment,the pseudo-boehmite layer has an average pore diameter from 2 to 30 nm.In a more preferred embodiment, the pseudo-boehmite layer has an averagepore diameter from 3 to 10 nm.

[0052] In one embodiment, the pseudo-boehmite layer of the separator hasa thickness of from 1 micron to 50 microns. In a preferred embodiment,the pseudo-boehmite layer has a thickness of from 1 micron to 25microns. In a more preferred embodiment, the pseudo-boehmite layer has athickness of from 2 microns to 15 microns.

[0053] In another embodiment of the present invention, thepseudo-boehmite layer further comprises a binder. In one embodiment, thebinder is present in an amount of 5 to 70% by weight of pseudo-boehmitein the pseudo-boehmite layer in the separator. In a preferredembodiment, the binder comprises polyvinyl alcohol, polyethylene oxide,polyvinyl pyrrolidone, copolymers of the foregoing, or a combinationthereof.

[0054] In one embodiment, the separator for use in an electric currentproducing cell comprises at least one microporous pseudo-boehmite layerin contact with at least one protective coating layer comprising apolymer and a silica. In a preferred embodiment, the silica of theprotective coating layer is a hydrophobic silica.

[0055] Another aspect of the invention pertains to an electrolyteelement for use in an electric current producing cell, the electrolyteelement comprising: (a) a separator; and, (b) an organic electrolyte;wherein, the separator comprises: (i) at least one microporouspseudo-boehmite layer, as described herein, in contact with (ii) atleast one protective coating layer, as described herein; and theelectrolyte is contained within pores of the separator. Suitablematerials for use as the electrolyte include liquid electrolytes, gelpolymer electrolytes, and solid polymer electrolytes. In one embodiment,the electrolyte is an organic electrolyte. In one embodiment, theelectrolyte is an aqueous electrolyte. In a preferred embodiment, theorganic electrolyte is a liquid electrolyte.

[0056] Still another aspect of the present invention pertains to amethod of forming a separator for use in electric current producingcells, wherein the separator comprises: (i) at least one microporouspseudo-boehmite layer, as described herein, in contact with (ii) atleast one protective coating layer, as described herein. In oneembodiment, wherein the protective coating layer comprises a polymer,the method comprises the steps of: (a) coating onto a substrate a firstliquid mixture, A, comprising a boehmite sol, or alternatively, coatingonto a substrate a first liquid mixture, B, comprising one or morepolymers, monomers, or macromonomers, to form a first coating layer; (b)drying the first coating layer formed in step (a) to form a microporouspseudo-boehmite layer, if the first liquid mixture A was utilized instep (a), or alternatively, drying the first coating layer formed instep (a) to form a protective coating layer, if the first liquid mixtureB was utilized in step (a), to form a dried first coating layer; (c)coating onto the layer formed in step (b) a second liquid mixture, B′,comprising one or more polymers, monomers, or macromonomers to form asecond coating layer, if a microporous pseudo-boehmite layer was formedin step (b), or alternatively, coating onto the layer formed in step (b)a second liquid mixture, A′, comprising a boehmite sol, if a protectivecoating layer was formed in step (b), to form a second coating layer;(d) drying the second coating layer formed in step (c) to form aprotective coating layer, if the second liquid mixture B′ was utilizedin step (c), or alternatively, to form a microporous pseudo-boehmitelayer, if the second liquid mixture A′ was utilized in step (c), to forma dried second coating layer. In one embodiment, subsequent to formationof a protective coating layer, there is a further step of curing thedried coating layer to form a cured protective coating layer by use ofan energy source. In one embodiment, the curing is performed using anenergy source selected from the group consisting of: heat, ultravioletlight, visible light, infrared radiation, and electron beam radiation.In one embodiment, after step (d), steps (a) and (b) are repeated toform a third coating layer. In one embodiment, after step (d), steps(a), (b), (c), and (d) are repeated to form a third coating layer and afourth coating layer.

[0057] In one embodiment, the polymers, monomers and macromonomers foruse in forming the protective coating layer have a molecular weightwhich is too large for impregnation into pores of the microporouspseudo-boehmite layer. In one embodiment, the polymers, monomers andmacromonomers have a molecular weight greater than 2000. In oneembodiment, the polymers, monomers and macromonomers have a molecularweight greater than 5000.

[0058] In one embodiment of the method, the monomers and macromonomersof the first or second liquid mixture comprising polymers, monomers andmacromonomers are selected from the group consisting of acrylates,methacrylates, olefins, epoxides, vinyl alcohols, vinyl ethers, andurethanes. In one embodiment, the acrylate monomer or macromonomer ofthe first or second liquid mixture is selected from the group consistingof polyethylene glycol diacrylates, polypropylene glycol diacrylates,ethoxylated neopentyl glycol diacrylates, ethoxylated bisphenol Adiacrylates, ethoxylated aliphatic urethane acrylates, and ethoxylatedalkylphenol acrylates.

[0059] In one embodiment, the monomers and macromonomers of the liquidmixture, B or B′, comprising one or more polymers, monomers ormacromonomers, are selected from monomers or macromonomers having theformula R¹(R²O)_(n)—R³, as described herein.

[0060] In one embodiment of the methods, the liquid mixture, B or B′,comprising one or more polymers, monomers or macromonomers, comprises apolymer. In one embodiment, one or more polymers of liquid mixture, B orB′, are selected from the group consisting of polyacrylates,polymethacrylates, polyolefins, polyurethanes, polyvinyl ethers,polyvinyl pyrrolidones, acrylonitrile-butadiene rubber,styrene-butadiene rubber, acrylonitrile-butadiene-styrene, sulfonatedstyrene/ethylene-butylene/styrene triblock polymers, and mixturesthereof.

[0061] In one embodiment of the method, the liquid mixture, B or B′,comprising one or more polymers, monomers or macromonomers, furthercomprises a second polymer. In one embodiment of the method, the liquidmixture, B or B′, comprising one or more polymers, monomers ormacromonomers, further comprises a pigment, as described herein.

[0062] In one embodiment, the liquid mixture, B or B′, comprising one ormore polymers,

[0063] In one embodiment of the methods, the liquid mixture, B or B′,further comprises one or more solvents selected from the groupconsisting of water, acetone, methyl ethyl ketone, acetonitrile,benzene, toluene, tetrahydrofuran, dioxane, chloroform, pentane, hexane,cyclohexane, methyl acetate, ethyl acetate, butyl acetate, and methylenechloride.

[0064] In one embodiment, the liquid mixture, B or B′, comprising one ormore polymers, monomers, or macromonomers, has a viscosity from 15 cP to5000 cP.

[0065] In one embodiment, the liquid mixture, A or B′, comprising aboehmite sol further comprises a binder, as described herein. In oneembodiment, the binder is present in the amount of 5 to 70% of weight ofthe pseudo-boehmite in the pseudo-boehmite layer.

[0066] In one embodiment of the methods, subsequent to step (d), thereis a further step of delaminating the separator from the substrate. Inone embodiment of the methods, subsequent to the third coating layer,there is a further step of delaminating the separator from thesubstrate. In one embodiment, at least one outermost surface of thesubstrate comprises a cathode active layer and the first liquid mixtureof step (a) is coated onto the cathode coating layer.

[0067] In another embodiment of the methods of the present invention offorming a separator for use in electric current producing cells, whereinthe separator comprises: (i) at least one microporous pseudo-boehmitelayer, in contact with (ii) at least one protective coating layer andwhere the protective coating layer is on the side of the separatoropposite from the cathode active layer in the cell the protectivecoating layer is formed by a physical deposition process or a chemicalvapor deposition process. In one embodiment, the protective coatinglayer comprises a single ion conducting glass conductive to lithiumions. In one embodiment, the single ion conducting glass is selectedfrom the group consisting of lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumtitanium oxides, lithium lanthanum oxides, lithium silicosulfides,lithium borosulfides, lithium aluminosulfides, lithium germanosulfides,and lithium phosphosulfides. In one embodiment, the protective coatinglayer comprises a conductive polymer selected from the group consistingof poly(p-phenylene), polyacetylene, poly(phenylenevinylene),polyazulene, poly(perinaphthalene), polyacenes, andpoly(naphthalene-2,6-diyl).

[0068] Yet another aspect of the present invention pertains to a methodof making an electrolyte element for an electric current producing cell,wherein the electrolyte element comprises a separator comprising: (i) atleast one microporous pseudo-boehmite layer in contact with (ii) atleast one protective coating layer; wherein the method comprises thesteps of forming a separator, as described herein for methods of forminga separator, and after formation of a separator, there is a further stepof contacting a surface of the separator with an electrolyte, asdescribed herein, thereby causing infusion of the electrolyte into poresof the separator. In one embodiment, the electrolyte is an organicelectrolyte. In one embodiment, the electrolyte is an aqueouselectrolyte.

[0069] In a preferred embodiment of the method for making an electrolyteelement, the organic electrolyte is a liquid electrolyte.

[0070] Still another aspect of the invention pertains to an electriccurrent producing cell, said cell comprising a cathode, an anode, and anelectrolyte element interposed between said cathode and said anode,wherein said electrolyte element comprises: (a) a separator; and, (b) anelectrolyte; wherein, said separator comprises: (i) at least onemicroporous pseudo-boehmite layer, as described herein, in contact with(ii) at least one protective coating layer, as described herein; and,said electrolyte, as described herein, is present within pores of saidseparator.

[0071] In one embodiment of the electric current producing cell, thecell is a secondary battery. In one embodiment of the electric currentproducing cell, the cell is a primary battery.

[0072] In one embodiment of the electric current producing cell, theanode active material is selected from the group consisting of lithiummetal, lithium-aluminum alloys, lithium-tin alloys, lithium-intercalatedcarbons, and lithium-intercalated graphites.

[0073] In one embodiment of the electric current producing cell, thecathode comprises a cathode active material selected from the groupconsisting of electroactive transition metal chalcogenides,electroactive conductive polymers, and electroactive sulfur-containingmaterials.

[0074] In one embodiment of the electric current producing cell, theelectroactive sulfur-containing material of the cathode compriseselemental sulfur. In one embodiment, the electroactive sulfur-containingmaterial comprises a sulfur-containing polymer comprising a polysulfidemoiety, S_(m), selected from the group consisting of covalent —S_(m)—moieties, ionic —S_(m) ⁻ moieties, and ionic S_(m) ²⁻ moieties, whereinm is an integer equal to or greater than 3. In one embodiment, m of thepolysulfide moiety, S_(m), of the sulfur-containing polymer is aninteger equal to or greater than 8. In one embodiment, thesulfur-containing polymer has polymer backbone chain and the polysulfidemoiety, S_(m), is covalently bonded by one or both of its terminalsulfur atoms on a side group to the polymer backbone chain. In oneembodiment, the sulfur-containing polymer has a polymer backbone chainand the polysulfide moiety, —S_(m),— is incorporated into the polymerbackbone chain by covalent bonding of terminal sulfur atoms of thepolysulfide moiety. In one embodiment, the sulfur-containing polymercomprises greater than 75 weight percent of sulfur.

[0075] A further aspect of the present invention pertains to a methodfor forming an electric current producing cell. The method comprisesproviding an anode, as described herein, and a cathode, as describedherein, and interposing an electrolyte element, as described herein,between the anode and the cathode. In one embodiment of the method forforming an electric current producing cell, the electrolyte of theelectrolyte element comprises one or more materials selected from thegroup consisting of liquid electrolytes, gel polymer electrolytes, andsolid polymer electrolytes, as described herein.

[0076] As will be appreciated by one of skill in the art, features ofone aspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077]FIG. 1 shows a sectional view of one embodiment of the separatorof the present invention comprising (a) a first layer 20 comprisingmicroporous pseudo-boehmite and (b) a second layer 30 of a protectivelayer, on a substrate 10 comprising a cathode active layer 15. Themicroporous pseudo-boehmite layer 20 contains a three-dimensionalnetwork of pores 50, and the protective coating layer 30 furthercomprises a pigment 60.

[0078]FIG. 2 shows a sectional view of one embodiment of the separatorof this invention as a free standing separator comprising (a) amicroporous pseudo-boehmite layer 20 and (b) a protective coating layer30. The pseudo-boehmite layer 20 contains a three-dimensional network ofpores 50, and the protective coating layer 30 further comprises apigment 60.

[0079]FIG. 3 shows a sectional view of one embodiment of the separatorof this invention comprising (a) a first layer 30 of a protectivecoating and (b) a second layer 20 comprising microporouspseudo-boehmite, on a substrate 10 comprising a cathode active layer 15.

[0080]FIG. 4 shows a sectional view of one embodiment of the separatorof this invention comprising (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, and (c)a third layer 22 comprising microporous pseudo-boehmite, on a substrate10 comprising a cathode active layer 15.

[0081]FIG. 5 shows a sectional view of one embodiment of the separatorof this invention comprising (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, and (c)a third layer 22 comprising microporous pseudo-boehmite, on a smoothrelease substrate 12.

[0082]FIG. 6 shows a sectional view of one embodiment of the separatorof this invention as a free standing separator comprising (a) amicroporous pseudo-boehmite layer 20, (b) a protective coating layer 30,and (c) a microporous pseudo-boehmite layer 22.

[0083]FIG. 7 shows a sectional view of one embodiment of the separatorof this invention comprising (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, (c) athird layer 22 comprising microporous pseudo-boehmite, and (d) a fourthlayer 15 of a cathode active layer, on a smooth release substrate 12.

[0084]FIG. 8 shows a sectional view of one embodiment of the separatorof this invention as a free standing separator and cathode active layercombination comprising (a) a microporous pseudo-boehmite layer 20, (b) aprotective coating layer 30, (c) a microporous pseudo-boehmite layer 22,and (d) a cathode active layer 15.

[0085]FIG. 9 shows a sectional view of one embodiment of the separatorof this invention comprising (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, (c) athird layer 22 comprising microporous pseudo-boehmite, and (d) a fourthlayer 34 of a protective coating, on a substrate 10 comprising a cathodeactive layer 15.

[0086]FIG. 10 shows a sectional view of one embodiment of the separatorof this invention as a free standing separator comprising (a) aprotective coating layer 30, (b) a microporous pseudo-boehmite layer 20,(c) a protective coating layer 34, (d) a microporous pseudo-boehmitelayer 22, and (e) a protective coating layer 38.

[0087]FIG. 11 shows a sectional view of one embodiment of the separatorof this invention as a free standing separator comprising (a) aprotective coating layer 30, (b) a microporous pseudo-boehmite layer 20,and (c) a protective coating layer 34.

DETAILED DESCRIPTION OF THE INVENTION

[0088] The separators of the present invention provide superior electriccurrent producing cell properties, particularly in cells utilizingseparators with thicknesses below about 25 microns. Suitable electriccurrent producing cells for use with the separator of the presentinvention include, but are not limited to, primary and secondarybatteries, capacitors including supercapacitors, fuel cells, andelectrochemical sensors and displays, including bipolar configurationsof batteries and capacitors, as these various electric current producingdevices are known in the art. Conventional separators, such as porouspolyolefins, porous fluoropolymers where the porosity is provided by asolvent extraction process, and glass fiber papers, and the like, aredifficult and costly to manufacture, especially at thicknesses belowabout 25 microns. Due to the nature of the processes used to manufacturethese separators and the relatively large pore sizes intrinsic to theseseparators, electrical shorting may be a significant challenge atseparator thicknesses of below about 25 microns, especially atthicknesses below about 15 microns. To overcome these limitations, theseparators of the present invention for use in electric currentproducing cells comprise (i) at least one microporous pseudo-boehmitelayer in contact with (ii) at least one protective coating layer.

[0089] Microporous pseudo-boehmite separator layers, as for example,described by Carlson et al. in copending U.S. patent application Ser.No. 08/995,089, to the common assignee, are effective in manyelectrochemical cell configurations. However, pseudo-boehmite separatorlayers may lack sufficient strength and flexibility to be configuredinto cells with, for example, a prismatic configuration. The separatorof the present invention provides an improvement whereby thepseudo-boehmite layer of the separator is coated, in one embodiment ofthe invention, with a protective coating layer comprising a polymer.This protective coating layer provides a protective layer which enhancesthe strength and adds flexibility to the pseudo-boehmite layer of theseparator. Electrochemical cells in a prismatic configuration, such asthose described in copending U.S. patent application Ser. No. 09/215,030to Thibault et al., to the common assignee, may be successfully builtwith, this protective coated pseudo-boehmite separator. Furthermore, theprotective coating layer is resistant to electrolytes.

[0090] Protective Coating Layer

[0091] The separators of the present invention comprises at least onemicroporous pseudo-boehmite layer wherein the separator is in contactwith at least one protective coating layer, and wherein at least one ofthe at least one protective coating layers is on the anode-facing sideof the separator opposite from the cathode active layer of the cell. Inembodiments wherein the protective coating layer comprises a polymer,the one or more protective coating layers enhance the strength and addflexibility to separators comprising one or more microporouspseudo-boehmite layers. When the protective coating layer is on the sideof the separator opposite from the cathode and when this layer will bein contact with the anode, the protective coating layer may additionallyfunction to reduce or eliminate undesirable degradation of the anode bythe electrolyte.

[0092] The protective coating layers of the present invention possess awide range of compositions including compositions which may haveporosity and compositions which may lack porosity but may be single ionconductors. The compositions which possess porosity may function as acomponent of a separator whereas those compositions which lack porositywill not function as a separator component.

[0093] In an assembled cell, the protective coating layer of theseparator may directly be in contact with the anode surface and therebyprovide protection for the anode. Although protection for the anode maybe provided, for example, by conductive polymer coating layers or singleion conductive coating layers coated on the anode, it may be moredesirable to coat the protective layers as a layer of the separator onthe side opposite from the cathode. This configuration in an assembledcell may more effectively accommodate the changes during charge anddischarge cycles of the cell, such as, for example, thickness changes ofthe anode during charge and discharge cycles.

[0094] The term “monomer” is used herein to describe the moieties whichhave a reactive moiety and are capable of reacting to form a polymer.

[0095] The term “polymer” is used herein to describe the molecules thathave two or more repeating moieties formed from a monomer moiety.

[0096] The term “macromonomer” is used herein to describe polymers withmolecular weights from several hundreds to tens of thousands with afunctional group at the chain end that may be polymerized.

[0097] The polymer of the protective coating layers of the separator ofthe present invention comprises one or more moieties from thepolymerization of one or more monomers or macromonomers. Examples ofsuitable monomers or macromonomers include, but are not limited to,acrylates, methacrylates, olefins, epoxides, vinyl alcohols, vinylethers, and urethanes.

[0098] Preferred olefinic monomers include, but are not limited to,ethylene, propylene, butene, pentene, hexene, octene, and styrene.

[0099] Preferred acrylate monomers or macromonomers include, but are notlimited to, polyethylene glycol diacrylates, polypropylene glycoldiacrylates, ethoxylated neopentyl is glycol diacrylates, ethoxylatedbisphenol A diacrylates, ethoxylated aliphatic urethane acrylates,ethoxylated alkylphenol acrylates, and alkylacrylates.

[0100] Further examples of suitable polymers for use in the protectivecoating layer are those comprising one or more moieties formed bypolymerization of one or more monomers or macromonomers selected fromthe group consisting of monomers and macromonomers having the formula:

R¹(R²O)_(n)-R³

[0101] wherein:

[0102] R¹ is the same or different at each occurrence and is selectedfrom the group consisting of

[0103] CH₂═CH(C═O)—O—,

[0104] CH₂═C(CH₃)(C═O)—O—,

[0105] CH₂═CH—,

[0106] CH₂═CH—O—;

[0107] R² is the same or different at each occurrence and is selectedfrom the group consisting of

[0108] —CH₂—CH₂—,

[0109] —CH(CH₃)—CH₂—,

[0110] —CH₂—CH₂—CH₂—,

[0111] —CH(C₂H₅)—CH₂—,

[0112] —CH₂—CH₂—CH₂—CH₂—;

[0113] R³ is the same or different at each occurrence and is selectedfrom the group consisting of

[0114] cyano, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl,2-ethylhexyl, decyl, dodecyl, phenyl, butylphenyl, octylphenyl,nonylphenyl, R¹, —X—(OR²)_(m)—R¹, —Y[(OR²)_(o)—R¹]₂, —Z[(OR²)_(p)—R¹]₃;

[0115] X is a divalent radical selected from the group consisting of

[0116] and

[0117]  —(CH₂)_(r)—, where r is 3, 4, or 6;

[0118] Y is a trivalent radical selected from the group consisting of

[0119] Z is a tetravalent radical selected from the group consisting of

[0120] m is an integer ranging from 0 to 100;

[0121] n is an integer ranging from 0 to 100;

[0122] o is an integer ranging from 0 to 100; and,

[0123] p is an integer ranging from 0 to 100.

[0124] Yet further examples of suitable polymers for use in theprotective coating layer include, but are not limited to, polyacrylates,polymethacrylates, polyolefins, polyurethanes, polyvinyl ethers,polyvinyl pyrrolidones, acrylonitrile-butadiene rubber,styrene-butadiene rubber, acrylonitrile-butadiene-styrene, sulfonatedstyrene/ethylene-butylene/styrene triblock polymers, and mixturesthereof.

[0125] The protective coating layer of the present invention enhancesthe properties of the one or more pseudo-boehmite layers, for example,it provides flexibility and toughness to the separator. At the same timethe protective coating layer should not negatively impact the desiredseparator properties of the one or more pseudo-boehmite layers. Suitablepolymeric protective coating layers should add flexibility and toughnessto the separator while at the same time allowing cations, such aslithium ions, to pass through the separator. In one embodiment, it ispreferred that the polymeric protective coating layer slow or inhibitthe passage of sulfide or polysulfide ions.

[0126] Multiphase polymers which are characterized by highly polarsegments and less polar segments possess these properties and can besuitable for the protective coating layers. Examples of multiphasepolymer structures include but are not limited to: (a) ethylene oxidepolydimethylsiloxane graft copolymers as described in U.S. Pat. No.5,362,493 to Skotheim et al.; (b) block copolymers, for example,sulfonated olefin/styrene polymers, such as sulfonatedstyrene/ethylene-butylene/styrene triblock copolymers, as described inU.S. Pat. Nos. 5,468,574 and 5,679,482 to Ehrenberg et al., whichcomprise ion conducting components and flexible connecting components;(c) polymer blends such as described in U.S. Pat. Nos. 5,585,039 and5,609,795 to Matsumoto et al.; and (d) graft copolymers such asacrylonitrile/butadiene/styrene polymers (ABS) as described in U.S. Pat.No. 4,064,116 to Papetti.

[0127] The polymer blends (c) include, but are not limited to,acrylonitrile-butadiene rubber, styrene-butadiene rubber, and mixturesthereof. These polymers are elastomeric and thermoplastic composites andmay possess toughness and good dimensional stability. By experimentationone skilled in the art can choose polymer blends with the desiredflexibility and toughness in the protective layer. Furthermore, thepolar nature of the highly polar segments, for example, from the nitrilefunction in acrylonitrile, allow cation passage needed for the separatorfunction.

[0128] In one embodiment, the protective coating layer on the separatorcomprises a single ion conductive layer, for example, including, but notlimited to, inorganic, organic and mixed organic-inorganic polymericmaterials. In one embodiment, the protective coating layer comprises asingle ion conductive glass conductive to lithium ions. Among thesuitable glasses are those that may be characterized as containing a“modifier” portion and a “network” portion, as known in the art. Themodifier is typically a metal oxide of the metal ion conductive in theglass. The network former is typically a metal chalcogenide, such as,for example, a metal oxide or metal sulfide. Suitable single ionconducting glasses include. but are not limited to, lithium silicates,lithium borates, lithium aluminates, lithium phosphates, lithiumphosphorus oxynitrides, lithium titanium oxides, lithium lanthanumoxides, lithium silicosulfides, lithium borosulfides, lithiumaluminosulfides, lithium germanosulfides, lithium phosphosulfides, andcombinations thereof.

[0129] In one embodiment, the protective coating layer comprises aconductive polymer. Suitable conductive polymers include those describedin U.S. Pat. No. 5,648,187 to Skotheim, for example, including, but notlimited to, poly(p-phenylene), polyacetylene, poly(phenylenevinylene),polyazulene, poly(perinaphthalene), polyacenes, andpoly(naphthalene-2,6-diyl).

[0130] Alternatively, the required porosity of the tough and flexibleprotective coating layer can be provided by dispersed polar finepigments in non-polar polymers, such as, for example, silica in olefinpolymers. Another approach to porosity in polymer coating layers is theformation of vesicular films. In a vesicular or voided structure thevoids or bubbles are produced by decomposing a vesiculating agent by,for example, uv irradiation to generate a gas such as nitrogen uponexposure to light with subsequent heating to expand the size of the voidor vesicle. Suitable vesiculating agents include a wide variety ofdiazo-compounds which liberate nitrogen upon exposure to light such asthe quinone-diazides, azides, and carbazide compounds described in U.S.Pat. No. 3,143,418 and conventional diazo-compounds such as thosementioned in U.S. Pat. No. 3,779,768. Suitable resins for producingvesicular coatings are described, for example, in U.S. Pat. No.4,302,524 to Mandella et al. and U.S. Pat. No. 4,451,550 to Bennett etal.

[0131] The molecular weight of the polymer of the protective coatinglayer is preferably greater than 10,000. More preferred is a polymer ofmolecular weight greater than 50,000.

[0132] The thickness of the protective coating layer comprising apolymer of the separator, may vary over a wide range from about 0.2microns to about 20 microns. In a preferred embodiment, the protectivecoating layer has a thickness of from about 0.5 microns to about 15microns. More preferred is a thickness of from about 0.5 microns toabout 10 microns, and even more preferred is a thickness of from about0.5 microns to about 5 microns, especially when multiple protectivecoating layers are present. The thickness of the single ion conductingprotective coating layer may vary over a wide range from about 5 nm toabout 5 microns. More preferably the single ion conducting protectivecoating layer has a thickness of from about 10 nm to about 2 microns.The thickness of the conductive polymer protective coating layer mayalso vary over a wide range from about 5 nm to about 5 microns. Morepreferably the conductive polymer protective coating layer has athickness of from about 10 nm to about 2 microns.

[0133] Conventional separators, such as polyolefin materials, aretypically 25 to 50 microns in thickness so it is particularlyadvantageous that the protective coated microporous separators of thisinvention can be effective and inexpensive at thicknesses well below 25microns. In other words, it is preferable that the combined thickness ofthe one or more pseudo-boehmite layers and the one or more protectivecoating layers be below 25 microns.

[0134] The protective coating layer comprising a polymer of theseparator of the present invention may further comprise a pigment.Suitable pigments for use in the polymer protective coating layerinclude, but are not limited to, colloidal silicas, amorphous silicas,surface treated silicas, colloidal aluminas, amorphous aluminas,conductive carbons, tin oxides, titanium oxides and polyethylene beads.Preferred pigments for use in the polymer protective coating layer arecolloidal silicas, amorphous silicas, surface treated silicas, or acombination thereof. Surface treated silicas, including hydrophobicsilicas, are especially preferred.

[0135] One embodiment of the separators of this invention is illustratedin FIG. 1, which shows a sectional view of the separator comprising (a)a first layer 20 comprising microporous pseudo-boehmite and (b) a secondlayer 30 of a protective coating, on a substrate 10 comprising a cathodeactive layer 15. As used herein, the term “cathode active layer” relatesto any layer in the cathode of an electric current producing cell whichcomprises a cathode active material. The pseudo-boehmite layer 20contains a three-dimensional network of pores 50, and the protectivecoating layer 30 further comprises a pigment 60. In one embodiment, asillustrated in FIG. 2, the separator of this invention is a freestanding separator comprising (a) a microporous pseudo-boehmite layer 20and (b) a protective coating layer 30. The pseudo-boehmite layer 20contains a three-dimensional network of pores 50, and the protectivecoating layer 30 further comprises a pigment 60.

[0136] The microporous pseudo-boehmite layers and the protective coatinglayers of the separators of the present invention may be coated in anyorder on the substrate. For example, as illustrated in FIG. 3, in oneembodiment, the separator comprises (a) a first layer 30 of a protectivecoating and (b) a second layer 20 comprising microporouspseudo-boehmite, on a substrate 10 comprising a cathode active layer 15.

[0137] U.S. Pat. No. 5,463,178 to Suzuki et al. describes an ink jetrecording sheet in which a substrate is coated with a porous layer ofpseudo-boehmite and a layer of silica is formed on the porous layer ofpseudo-boehmite. The silica layer is stated to provide improved abrasionresistance to the recording sheet, but no requirement for a polymer inthe layer of silica or for durability during winding and folding, suchas occurs in the fabrication of electric current producing cells, isdescribed.

[0138] The weight ratio of the polymer to the pigment in the protectivecoating layer may vary from about 1:10 to about 10:1. In a preferredembodiment, the polymer and the pigment are present in the protectivecoating layer at a weight ratio of from about 1:4 to about 6:1. In amore preferred embodiment, the polymer and the pigment are present inthe protective coating layer at a weight ratio of from about 1:3 toabout 4:1.

[0139] The particle size or diameter of the pigment is preferably largerthan the average pore diameter of the pseudo-boehmite layer so that thepigment does not penetrate pores of the pseudo-boehmite layer, in thosecases where the protective coating layer comprises a pigment and iscoated onto a microporous pseudo-boehmite layer. The particle size ofthe pigment may range from about 10 nm to about 10,000 nm. In apreferred embodiment, the pigment has a particle size from about 20 nmto about 6,000 nm. In a most preferred embodiment, the pigment has aparticle size from about 50 nm to about 3,000 nm.

[0140] In addition to polymer and pigments, the protective coating layerof the separators of the present invention may further comprise otheradditives as are known in the art for coatings, especially those knownfor use in flexible and durable coatings. Examples of suitable otheradditives include, but are not limited to, photosensitizers forradiation curing of any monomers and macromonomers present, catalystsfor non-radiation curing of any monomers, macromonomers, or polymerspresent, crosslinking agents such as zirconium compounds, aziridines,and isocyanates, surfactants, plasticizers, dispersants, flow controladditives, and rheology modifiers.

[0141] Microporous Pseudo-boehmite Layer

[0142] Microporous pseudo-boehmite layers for use as separators inelectrochemical cells are described in copending U.S. patent applicationSer. Nos. 08/995,089 and 09/215,112, both to Carlson et al., of thecommon assignee.

[0143] The term “pseudo-boehmite,” as used herein, pertains to hydratedaluminum oxides having the chemical formula Al₂O₃.xH₂O wherein x is inthe range of from 1.0 to 1.5. Terms used herein, which are synonymouswith “pseudo-boehmite,” include “boehmite,” “AlOOH,” and “hydratedalumina.” The materials referred to herein as “pseudo-boehmite” aredistinct from anhydrous aluminas (Al₂O₃, such as alpha-alumina andgamma-alumina), and hydrated aluminum oxides of the formula Al₂O₃.xH₂Owherein x is less than 1.0 or greater than 1.5.

[0144] The term “microporous,” is used herein to describe the materialof a layer, which material possesses pores of diameter of about 10microns or less which are connected in a substantially continuousfashion from one outermost surface of the layer through to the otheroutermost surface of the layer. Porous separators which are made fromfibers, such as glass, TEFLON (a trademark for polytetrafluoroethyleneavailable from DuPont Corporation, Wilmington, Del.), and polypropylene,are generally characterized as non-woven separator materials and havepore diameters too large to be called microporous, thereby making themunacceptable for rechargeable cells where dendrite formation is apotential concern.

[0145] The amount of these pores in the layer may be characterized bythe pore volume, which is the volume in cubic centimeters of pores perunit weight of the layer. The pore volume may be measured by filling thepores with a liquid having a known density and then calculated by theincrease in weight of the layer with the liquid present divided by theknown density of the liquid and then dividing this quotient by theweight of the layer with no liquid present, according to the equation:$\begin{matrix}{{{Pore}\quad {Volume}} = \frac{\left\lbrack {W_{1} - W_{2}} \right\rbrack/d}{W_{2}}} & I\end{matrix}$

[0146] where W₁ is the weight of the layer when the pores are completelyfilled with the liquid of known density, W₂ is the weight of the layerwith no liquid present in the pores, and d is the density of the liquidused to fill the pores. Also, the pore volume may be estimated from theapparent density of the layer by subtracting the reciprocal of thetheoretical density of the materials (assuming no pores) comprising themicroporous layer from the reciprocal of the apparent density ormeasured density of the actual microporous layer, according to theequation: $\begin{matrix}{{{Pore}\quad {Volume}} = \left( {\frac{1}{d_{1}} - \frac{1}{d_{2}}} \right)} & {II}\end{matrix}$

[0147] where d₁ is the density of the layer which is determined from thequotient of the weight of the layer and the layer volume as determinedfrom the measurements of the dimensions of the layer, and d₂ is thecalculated density of the materials in the layer assuming no pores arepresent or, in other words, d₂ is the density of the solid part of thelayer as calculated from the densities and the relative amounts of thedifferent materials in the layer. The porosity or void volume of thelayer, expressed as percent by volume, can be determined according tothe equation: $\begin{matrix}{{Porosity} = \frac{100\left( {{Pore}\quad {Volume}} \right)}{\left\lbrack {{{Pore}\quad {Volume}} + {1/d_{2}}} \right\rbrack}} & {III}\end{matrix}$

[0148] where pore volume is as determined above, and d₂ is thecalculated density of the solid part of the layer, as described above.

[0149] In one embodiment, the microporous pseudo-boehmite layer of theseparator of the present invention has a pore volume from 0.02 to 2.0cm³/g. In a preferred embodiment, the microporous pseudo-boehmite layerhas a pore volume from 0.3 to 1.0 cm³/g. In a more preferred embodiment,the microporous pseudo-boehmite layer has a pore volume from 0.4 to 0.7cm³/g. Below a pore volume of 0.02 cm³/g, the transport of ionic speciesis inhibited by the reduced pore volume. Above a pore volume of 2.0cm³/g, the amount of voids are greater which reduces the mechanicalstrength of the microporous pseudo-boehmite layer.

[0150] In contrast to conventional microporous separators whichtypically have pore diameters on the order of 1 to 1 0 microns, themicroporous pseudo-boehmite layers of the separator of the presentinvention have pore diameters which range from about 1 micron down toless than 0.002 microns. Microporous separator layers, such as themicroporous pseudo-boehmite layers of the present invention, with porediameters in the range of about 1 micron (100 nm) down to less than0.002 microns (2 nm) are also commonly referred to in the art 67 asnanoporous materials. In one embodiment, the microporous pseudo-boehmitelayer has an average pore diameter from 0.001 microns or 1 nm to 0.3microns or 300 nm. In a preferred embodiment, the microporouspseudo-boehmite layer has an average pore diameter from 2 nm to 30 nm.In a more preferred embodiment, the microporous pseudo-boehmite layerhas an average pore diameter from 3 nm to 10 nm.

[0151] One distinct advantage of separators with much smaller porediameters on the order of 0.001 to 0.03 microns is that insolubleparticles, even colloidal particles with diameters on the order of 0.05to 1.0 microns, can not pass through the separator because of theultrafine pores. In contrast, colloidal particles, such as theconductive carbon powders often incorporated into cathode compositions,can readily pass through conventional separators, such as microporouspolyolefins, and thereby can migrate to undesired areas of the cell.

[0152] Another significant advantage of the separators of the presentinvention comprising a microporous pseudo-boehmite layer overconventional separators is that the nanoporous structure of themicroporous pseudo-boehmite layer may function as an ultrafiltrationmembrane and, in addition to blocking all particles and insolublematerials, may block or significantly inhibit the diffusion of solublematerials of relatively low molecular weights, such as 2,000 or higher,while permitting the diffusion of soluble materials with molecularweights below this cutoff level. This property may be utilized toadvantage in selectively impregnating or imbibing materials into theseparator layers during manufacture of the electric current producingcell or in selectively permitting diffusion of very low molecular weightmaterials through the separator during all phases of the operation ofthe cell while blocking or significantly inhibiting the diffusion ofinsoluble materials or of soluble materials of medium and highermolecular weights.

[0153] Another important advantage of the extremely small pore diametersof the separators of the present invention is the strong capillaryaction of the tiny pores in the pseudo-boehmite layer which enhances thecapability of the separators to readily take up or imbibe electrolyteliquids and to retain these materials in the pores.

[0154] The microporous pseudo-boehmite layer may optionally furthercomprise a variety of binders to improve the mechanical strength and/orother properties of the layer, as for example, described in the twoaforementioned copending U.S. patent applications, both to Carlson etal. of the common assignee. Any binder that is compatible with theboehmite sol during mixing and processing into the microporous layer andprovides the desired mechanical strength and uniformity of the layerwithout significantly interfering with the desired microporosity issuitable for use. The preferred amount of binder is from 5% to 70% ofthe weight of the pseudo-boehmite in the layer. Below 5 weight percent,the amount of binder is usually too low to provide a significantincrease in mechanical strength. Above 70 weight percent, the amount ofbinder is usually too high and fills the pores to an excessive extentwhich may interfere with the transport of low molecular weight materialsthrough the microporous layer. The binder may be inorganic, such as forexample, silicas, gamma aluminum oxides, and alpha aluminum oxides, thatare known to typically form gel matrix structures with pseudo-boehmitepresent, for example, as is known in the art of microporous sol gel inkreceptive layers for inkjet printing. Preferably, the binders in themicroporous pseudo-boehmite layer are organic polymer binders. Examplesof suitable binders include, but are not limited to, polyvinyl alcohols,polyethylene oxides, polyvinyl pyrrolidones, copolymers thereof, andmixtures thereof. Binders may be water soluble polymers and may haveionically conductive properties. Further preferred binders may alsocomprise plasticizer components such as, but not limited to, lowmolecular weight polyols, polyalkylene glycols, and methyl ethers ofpolyalkylene glycols to enhance the coating, drying and flexibility ofthe pseudo-boehmite layer.

[0155] The thickness of the microporous pseudo-boehmite layer, with orwithout additional binder, for use in the separator of the presentinvention may vary over a wide range since the basic properties ofmicroporosity and mechanical integrity are present in layers of a fewmicrons in thickness as well as in layers with thicknesses of hundredsof microns. For various reasons including cost, overall performanceproperties of the separator, and ease of manufacturing, the desirablethicknesses of the microporous pseudo-boehmite layer are in the range of1 micron to 50 microns. Preferred are thicknesses in the range of 1micron to 25 microns. The more preferred thicknesses are in the range of2 microns to 15 microns. The most preferred thicknesses are in the rangeof 5 microns to 15 microns. Conventional separators, such as the porouspolyolefin materials, are typically 25 to 50 microns in thickness so itis particularly advantageous that the microporous separators of thisinvention can be effective and inexpensive at thicknesses well below 25microns.

[0156] The separators of this invention comprising a protective coatedmicroporous pseudo-boehmite layer essentially retain the desirableproperties of the uncoated pseudo-boehmite separator as described byCarlson et al. in the two aforementioned copending U.S. patentapplications to the common assignee. These include blocking particlesand insoluble materials, blocking or inhibiting the diffusion of solublematerials of relatively low molecular weights, such as 2,000 or higher,while permitting the diffusion of soluble materials with molecularweights below this cutoff level. Desirable properties also includepermitting the diffusion of soluble materials especially electrolytecations such as lithium ions. In other words, in a preferred embodiment,the polymer coating does not significantly modify the ability of themicroporous pseudo-boehmite layer to allow the flow of desirablematerials but may inhibit or at least slow the flow of undesirablematerials.

[0157] Separators with Multiple Microporous Pseudo-boehmite Layersand/or Protective Coating Layers

[0158] The separators of the present invention may have more than onemicroporous pseudo-boehmite layer, for example, as illustrated in FIGS.4 to 10. Also, the separators of the present invention may have morethan one protective coating layer, for example, as illustrated in FIGS.9 to 11. The compositions of these multiple microporous pseudo-boehmitelayers may be the same or different for each such layer in theseparator. Also, the compositions of these multiple protective coatinglayers may be the same or different for each such layer in theseparator.

[0159] In one embodiment, as illustrated in FIG. 4, the separator ofthis invention comprises (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, and (c)a third layer 22 comprising microporous pseudo-boehmite, on a substrate10 comprising a cathode active layer 15. When the separator of thisinvention is subsequently utilized as a free standing separator, theseparator may be conveniently formed on a release substrate, asillustrated in FIG. 5, from which it may be delaminated to provide afree standing separator, as shown in FIG. 6. In one embodiment, asillustrated in FIG. 5, the separator of the present invention comprises(a) a first layer 20 comprising microporous pseudo-boehmite, (b) asecond layer 30 of a protective coating, and (c) a third layer 22comprising microporous pseudo-boehmite, on a smooth release substrate12. In one embodiment, as illustrated in FIG. 6, the separator of thisinvention comprises (a) a microporous pseudo-boehmite layer 20, (b) aprotective coating layer 30, and (c) a microporous pseudo-boehmite layer22.

[0160] As another example of the wide variety of options for designs ofthe layers of the separators of the present invention and of the orderof these layers relative to a substrate or to a cathode active layer,FIG. 7 shows a sectional view of one embodiment of the separators ofthis invention comprising (a) a first layer 20 comprising microporouspseudo-boehmite, (b) a second layer 30 of a protective coating, (c) athird layer 22 comprising microporous pseudo-boehmite, and (d) a fourthlayer 15 of a cathode active layer, on a smooth release substrate 12.Also, the separator illustrated in FIG. 7 may be delaminated to providea free standing separator and cathode active layer combination, as shownin FIG. 8. In one embodiment, as illustrated in FIG. 8, the separator ofthe present invention comprises a separator and cathode active layercombination comprising (a) a microporous pseudo-boehmite layer 20, (b) aprotective coating layer 30, (c) a microporous pseudo-boehmite layer 22,and (d) a cathode active layer 15.

[0161] The separators of the present invention may comprise two or moremicroporous pseudo-boehmite layers and two or more protective coatinglayers, as, for example, illustrated in FIGS. 9 to 11. In oneembodiment, as illustrated in FIG. 9, the separator of this inventioncomprises (a) a first layer 20 comprising microporous pseudo-boehmite,(b) a second layer 30 of a protective coating, (c) a third layer 22comprising microporous pseudo-boehmite, and (d) a fourth layer 34 of aprotective coating comprising a polymer, on a substrate 10 comprising acathode active layer 15. Also, for example, in one embodiment, asillustrated in FIG. 10, the separator of the present invention is a freestanding separator comprising (a) a protective coating layer 30, (b) amicroporous pseudo-boehmite layer 20, (c) a protective coating layer 34,(d) a microporous pseudo-boehmite layer 22, and (e) a protective coatinglayer 38 comprising a polymer. Also, for example, in another embodiment,as illustrated in FIG. 11, the separator of the present invention is afree standing separator comprising (a) a protective coating layer 30,(b) a microporous pseudo-boehmite layer 20, and (c) a protective coatinglayer 34.

[0162] As a further example of the options for designs of the layers ofthe separator of the present invention, and of the relative order of thepseudo-boehmite layers and protective coating layers, two or more layersof one type may be in contact with each other, as for example,illustrated by the two protective layers overlying a pseudo-boehmitelayer described in Example 10.

[0163] Yet another example of the options for designs of the separatorfor use in an electrochemical cell of the present invention, is anembodiment in which a microporous pseudo-boehmite layer is in contactwith a protective coating layer upon which is coated a second protectivecoating layer; wherein the protective coating layers are on the side ofthe separator opposite from the cathode active layer of the cell. In oneembodiment, the second protective coating layer is a single ionconducting layer, preferably a single ion conducting glass.

[0164] Methods for Forming Separators

[0165] One aspect of the present invention pertains to methods of makinga separator comprising (i) at least one microporous pseudo-boehmitelayer in contact with (ii) at least one protective coating layer, foruse in electric current producing cells which overcomes thedisadvantages of the aforementioned conventional methods for formingseparators.

[0166] In one aspect of the method of the present invention to form aseparator comprising (i) at least one microporous pseudo-boehmite layerin contact with (ii) at least one protective coating layer, as describedherein. In one embodiment, wherein the protective coating layercomprises a polymer, the method comprises the steps of: (a) coating ontoa substrate a first liquid mixture, A, comprising a boehmite sol, oralternatively, coating onto a substrate a first liquid mixture, B,comprising one or more polymers, monomers, or macromonomers, to form afirst coating layer; (b) drying the first coating layer formed in step(a) to form a microporous pseudo-boehmite layer, if the first liquidmixture A was utilized in step (a), or alternatively, drying the firstcoating layer formed in step (a) to form a protective coating layer, ifthe first liquid mixture B was utilized in step (a), to form a driedfirst coating layer; (c) coating onto the layer formed in step (b) asecond liquid mixture, B′, comprising one or more polymers, monomers, ormacromonomers to form a second coating layer, if a microporouspseudo-boehmite layer was formed in step (b), or alternatively, coatingonto the layer formed in step (b) a second liquid mixture, A′,comprising a boehmite sol, if a protective coating layer was formed instep (b), to form a second coating layer; (d) drying the second coatinglayer formed in step (c) to form a protective coating layer, asdescribed herein, if the second liquid mixture B′ was utilized in step(c), or alternatively, to form a microporous pseudo-boehmite layer, asdescribed herein, if the second liquid mixture A′ was utilized in step(c), to form a dried second coating layer.

[0167] In one embodiment, subsequent to formation of a protectivecoating layer, the methods further comprise curing the dried protectivecoating layer to form a cured protective coating layer. The driedcoating layer may be cured to form a cured protective coating layercomprising a cured polymer by treatment with an energy source. Suitableenergy sources include, but are not limited to, heat, ultraviolet light,visible light, infrared radiation, and electron beam radiation. In oneembodiment, after step (d), steps (a) and (b) are repeated to form athird coating layer. Examples of separators that may be formed by thismethod of forming a third coating layer are illustrated by FIGS. 4 to 8and 11. In one embodiment, after step (d), steps (a), (b), (c), and (d)are repeated to form a third coating layer and a fourth coating layer.An example of separators that may be formed by this method of forming athird coating layer and a fourth coating layer is illustrated in FIG. 9.In one embodiment, steps, (a), (b), (c), (d), (a) and (b) are repeatedto form a third coating layer, a fourth coating layer, and a fifthcoating layer, as illustrated, for example in FIG. 10.

[0168] Examples of suitable monomers and macromonomers for use in theliquid mixture to form the protective coating layer include, but are notlimited to, acrylates, methacrylates, olefins, epoxides, vinyl alcohols,vinyl ethers, and urethanes. Suitable acrylate monomers andmacromonomers, include but are not limited to, compounds selected fromthe group consisting of: polyethylene glycol diacrylates, polypropyleneglycol diacrylates, ethoxylated neopentyl glycol diacrylates,ethoxylated bisphenol A diacrylates, ethoxylated aliphatic urethaneacrylates, and ethoxylated alkylphenol acrylates. Further, the monomersand macromonomers of the liquid mixture may be selected from monomersand macromonomers having the formula R¹(R²O)_(n)-R³, as describedherein, to form the protective coating layer.

[0169] The molecular weight of the monomers and macromonomers of theliquid mixture may be selected so that the liquid mixture to form theprotective coating layer does not significantly impregnate into pores ofthe microporous pseudo-boehmite layer, in those cases where the liquidmixture to form a protective coating layer is coated onto a microporouspseudo-boehmite layer. In a preferred embodiment, the molecular weightof the monomers and macromonomers is greater than 2000. In a morepreferred embodiment, the molecular weight of the monomers andmacromonomers is greater than 5000.

[0170] In one embodiment, the second liquid mixture, B or B′, maycomprise a solvent. The solvent may be aqueous or non-aqueous. Suitablesolvents include, but are not limited to, water, acetone, methyl ethylketone, acetonitrile, benzene, toluene, tetrahydrofuran, dioxane,chloroform, pentane, hexane, cyclohexane, methyl acetate, ethyl acetate,butyl acetate, and methylene chloride. In one embodiment, the solvent ofthe liquid mixture may comprise one or more of the monomers of thepresent invention.

[0171] In one embodiment, the liquid mixture to form the protectivecoating layer is in the form of a polymer latex. The term “latex,” asused herein, pertains to a stable colloidal dispersion of a polymericsubstance in an aqueous medium.

[0172] The penetration of the liquid mixture to form the protectivecoating layer into pores of the microporous pseudo-boehmite layer mayalso be controlled by selecting the viscosity of the liquid mixture. Forexample, an additive, such as a polymer may be added to the liquidmixture that forms the protective coating layer to increase theviscosity and to inhibit or slow the penetration of the liquid mixtureinto pores of the pseudo-boehmite layer. Examples of polymer additivesinclude, but are not limited to, polyacrylates, polymethacrylates,polyurethanes, polyolefins, for example, ethylene-propylene polymers,and cellulosics. Alternatively, for example, additional solvent may beused to lower the viscosity of the liquid mixture. Preferably, theliquid mixture to form the protective coating layer has a viscosity inthe range of 15 cP to 5000 cP. Besides particle size, molecular weight,and viscosity, other approaches to prevent or minimize the penetrationof the liquid mixture that forms the protective coating layer into poresof the microporous pseudo-boehmite layer include, but are not limitedto, prewetting the pseudo-boehmite layer with a solvent to hold out theprotective coating layer during the coating and drying steps.

[0173] Where there is a defect, such as a small crack, in themicroporous pseudo-boehmite layer, the liquid mixture to form theprotective coating layer may be advantageously utilized to penetrateinto the defect areas of the pseudo-boehmite layer to repair the defectswhere this is beneficial. This is one of the advantages of the methodsof forming a separator of the present invention.

[0174] If increased mechanical strength or some other improvement in theproperties of the protective coating layer of the separator is desired,the coating liquid mixture to form the protective coating layer mayfurther comprise a pigment, and the resulting protective coating layeris dried and optionally cured to form the protective coated microporouspseudo-boehmite separator. Suitable pigments for use in the protectivecoating layer include, but are not limited to, colloidal silicas,amorphous silicas, surface treated silicas, colloidal aluminas,amorphous aluminas, conductive carbons, graphites, tin oxides, titaniumoxides and polyethylene beads. Preferred pigments for use in the polymerprotective coating layer are colloidal silicas, amorphous silicas,surface treated silicas, or a combination thereof. Surface treatedsilicas, including hydrophobic silicas. are especially preferred.

[0175] The single ion conducting glass protective coating layer or theconductive polymer protective coating layer may be deposited on thesubstrate by techniques such as physical deposition, for example, bysputtering or evaporation, and chemical vapor deposition, for example,by plasma enhanced chemical vapor deposition. These protective coatinglayers may be advantageously applied to allow only lithium ions to reachthe anode surface. Other protective coating layers comprising single ionconductive layers may be deposited as sol gel formulations by methodsknown in the art for coating sol gel layers.

[0176] If increased mechanical strength or some other improvements suchas improved adhesion to the substrate or coating uniformity is desiredin the microporous pseudo-boehmite layer, the liquid mixture comprisinga boehmite sol may further comprise a binder, as described herein, andthen dried to form a microporous pseudo-boehmite layer with binderpresent. The types of the binders such as polyvinyl alcohols, theamounts of the binder materials, such as, in the range of 5 to 70% ofthe weight of the pseudo-boehmite in the layer, and the thicknesses ofthe microporous pseudo-boehmite layer with binder in the range of I to50 microns, preferably 1 to 25 microns, more preferably 2 to 15 microns,and most preferably 5 to 15 microns, are as described herein for themicroporous pseudo-boehmite separator.

[0177] These methods of forming a separator comprising (i) at least onemicroporous pseudo-boehmite layer with or without a binder present inthe pseudo-boehmite layer, as described herein, in contact with (ii) atleast one protective polymer coating, as described herein, may be usedto produce either a free standing separator or a separator coateddirectly onto a layer of an electric current producing cell. The freestanding separator may then be wound or otherwise fabricated into anelectric current producing cell. Also, the free standing separator maybe laminated to another layer of the electric current producing cell. Inone embodiment of the methods of forming the separators of thisinvention, wherein the protective coating layer comprises a polymer, theseparator is coated directly onto the cathode active layer of thecathode of the electric current producing cell by (a) application of afirst liquid mixture, A, comprising a boehmite sol or, alternatively, afirst liquid mixture, B, comprises one or more polymers, monomers ormacromonomers for forming a protective coating layer, onto the outermostsurface of a cathode coating on a suitable current collector substrate;(b) drying this first liquid coating layer formed in step (a) to form amicroporous pseudo-boehmite separator layer, as described herein, oralternatively, drying the first coating layer formed in step (a) to forma protective coating layer, as described herein; (c) coating onto thelayer formed in step (b) a second liquid mixture, B′, comprising one ormore polymers, monomers, or macromonomers to form a second coatinglayer, if a microporous pseudo-boehmite layer was formed in step (b), oralternatively, coating onto the layer formed in step (b) a second liquidmixture, A′, comprising a boehmite sol, if a protective coating layerwas formed in step (b), to form a second coating layer; (d) drying thesecond coating layer formed in step (c) to form a protective coatinglayer, as described herein, if the second liquid mixture B′ was utilizedin step (c), or alternatively, to form a microporous pseudo-boehmitelayer, as described herein, if the second liquid mixture A′ was utilizedin step (c), to form a dried second coating layer, as described herein.Optionally, subsequent to the formation of a protective coating layerthe methods may further comprise curing the dried protective coatinglayer to form a cured protective coating layer, as described herein. Ifthe protective coating layer further comprises a pigment, one embodimentof the separator formed by this method is illustrated in FIG. 1. If theprotective coating layer is applied first to the substrate and furthercomprises a pigment, one embodiment of the separator formed by thismethod is illustrated in FIG. 3.

[0178] In another embodiment, a free standing separator is formed byapplication of: (a) a first liquid mixture, A, comprising a boehmite solor, alternatively, a first liquid mixture, B, comprises one or morepolymers, monomers or macromonomers for forming a protective coatinglayer, onto the outermost surface of a cathode coating on a suitablecurrent collector substrate; (b) drying this first liquid coating layerformed in step (a) to form a microporous pseudo-boehmite separatorlayer, as described herein, or alternatively, drying the first coating,layer formed in step (a) to form a protective coating layer, asdescribed herein; (c) coating onto the layer formed in step (b) a secondliquid mixture, B′, comprising one or more polymers, monomers, ormacromonomers to form a second coating layer, if a microporouspseudo-boehmite layer was formed in step (b), or alternatively, coatingonto the layer formed in step (b) a second liquid mixture, A′,comprising a boehmite sol, if a protective coating layer was formed instep (b), to form a second coating layer; (d) drying the second coatinglayer formed in step (c) to form a protective coating layer, asdescribed herein, if the second liquid mixture B′ was utilized in step(c), or alternatively, to form a microporous pseudo-boehmite layer, asdescribed herein, if the second liquid mixture A′ was utilized in step(c), to form a dried second coating layer; and, then (e) delaminatingthe coated separator multilayer structure formed in the previous stepfrom the substrate to provide a free standing separator comprising oneor more microporous pseudo-boehmite layers in contact with one or moreprotective coating layers, as described herein. Optionally, subsequentto the formation of a protective coating layer the methods may furthercomprise curing the dried protective coating layer to form a curedprotective coating layer, as described herein. If the protective coatinglayer further comprises a pigment, one embodiment of the separatorformed by this method is illustrated in FIG. 2. The substrate isselected to have weak adhesion to the first coated layer so that theseparator coating may be readily delaminated from the substrate withoutdamaging the separator. Suitable substrates include, but are not limitedto, papers with release coatings, such as silicones, fluorocarbons, andpolyolefins, on the surface that receives the first liquid mixture andflexible plastic films, such as polyester and polystyrene films, eitheruntreated or with release coatings on the surface that receives thefirst liquid mixture. The width of the coated separator when it isdelaminated from the substrate may be the full width as coated on thesubstrate or the coated separator may be slit to a narrower width, suchas the width desired for use in the specific electric current producingcell, before it is delaminated from the substrate.

[0179] After delamination of the coated separator, the resulting freestanding coated separator may be utilized directly to form an electriccurrent producing cell using methods known in the art of fabricatingcells with free standing separators. Alternatively, for example. asecond protective coating layer may be applied to the uncoated side ofthe pseudo-boehmite layer of the free standing separator; and/or thefree standing coated separator may be laminated to a cathode activelayer on a substrate, to a cathode active layer and a cathode currentcollector, to an anode, or to an anode and anode current collector,prior to fabrication into an electric current producing cell.

[0180] A further distinct advantage of the methods to produce aseparator of the present invention is the flexibility in the coatingpatterns in which the separator layer may be applied to the substrate.For example, the separator layers may be applied over the entireoutermost surface of the cathode including the top surface and sides ofthe cathode active layer on the current collector and cathode substrate.The cathode active layer may thus be completely encapsulated on alloutermost surfaces, including the edges or sides of the cathode activelayer which are not contacted or covered by conventional free standingpolyolefin or other porous separators, by coating the separator layersin a pattern over all the outermost, exposed surfaces of the cathodeactive layer. This complete encapsulation by the separator layers of thepresent invention is very advantageous to safety and battery performancein providing an insulating surface to prevent any short circuits by thecathode during fabrication and during the use of the electric currentproducing cell. This encapsulation is also very advantageous to highcell capacity and long cycle life in acting as a barrier in blocking orinhibiting the migration of any insoluble or high molecular weightspecies in the cathode active layer to outside the cathode area andsimilarly in retarding the diffusion of any low molecular weightspecies, such as soluble polysulfides, in the cathode active layer tooutside the cathode area.

[0181] Electrolyte Elements and Methods of Preparing Same

[0182] The present invention provides an electrolyte element for use inan electric current producing cell, by combining the separator of thepresent invention, as described herein, with an electrolyte containedwithin the pores of the separator. The electrolyte may be any of thetypes of non-aqueous and aqueous electrolytes known in the art.

[0183] One aspect of the methods of making electrolyte elements for anelectric current producing cell of the present invention comprises thesteps of: (a) coating a first liquid mixture, as described herein, ontoa substrate; (b) drying the first coating layer, as described herein;(c) coating on the first coating layer formed in step (b) a secondliquid mixture, as described herein; (d) drying this second coatinglayer, as described herein, to form a separator layer comprising aprotective coating layer comprising a polymer in contact with amicroporous pseudo-boehmite layer, as described herein in the methods ofmaking a separator; and, (e) subsequently contacting the surfaces ofthis protective coated microporous pseudo-boehmite layer with anelectrolyte, preferably an organic electrolyte, thereby causing infusionof the electrolyte into pores of the separator. Optionally, after theformation of the protective coating layer and prior to step (e), theprotective coating layer may be cured by an energy source, to form acured protective coated separator, as described herein. Prior to theinfusion of the electrolyte, the microporous pseudo-boehmite layertypically has a pore volume from 0.02 to 2.0 cm³/g and an average porediameter from 1 nm to 300 nm, as described herein for the microporouspseudo-boehmite separator.

[0184] If increased mechanical strength or some other improvements suchas improved adhesion to the substrate or coating uniformity is desired,the coating liquid mixture comprising a boehmite sol, as describedherein, may further comprise a binder and then is dried to form amicroporous pseudo-boehmite layer with binder present, as describedherein. The coating liquid mixture comprising a polymer, monomer ormacromonomer may further comprise a pigment, a second polymer, or otheradditive, as described herein.

[0185] In a preferred embodiment, the method of producing theelectrolyte element comprises (a) providing a substrate with a cathodeactive layer on at least one of its outermost surfaces; (b) coating afirst liquid mixture onto this cathode active layer; (c) drying thisfirst coating layer formed in step (b) to form a microporous pseudoboehmite layer, as described herein, or alternatively, a protectivecoated layer comprising a polymer, as described herein; (d) coating ontothe first coating layer a second liquid mixture, as described herein;(e) drying this second coating layer formed in step (d) to form aprotective coated microporous pseudo-boehmite separator; and (f)contacting the surfaces of the protective coated microporouspseudo-boehmite separator with an organic electrolyte thereby causinginfusion of the electrolyte into pores of the separator. Optionally,after formation of the protective coating layer and before step (f),there is a step of curing the protective coating layer comprising apolymer, as described herein.

[0186] The electrolyte used in the present invention functions as amedium for storage and transport of ions, and may be any of the types ofelectrolytes known in the art of electric current producing cells. Anyliquid, solid, or solid-like material capable of storing andtransporting ions may be used, so long as the material is sufficientlychemically and electrochemically stable with respect to the anode andthe cathode and the material facilitates the transportation of ionsbetween the anode and the cathode without providing electricalconductivity that might cause a short circuit between the anode and thecathode.

[0187] Examples of suitable electrolytes for use in the electrolyteelements of the present invention include, but are not limited to,organic electrolytes comprising one or more electrolytes selected fromthe group consisting of liquid electrolytes, gel polymer electrolytes,and solid polymer electrolytes.

[0188] Examples of useful liquid electrolytes include, but are notlimited to, those comprising one or more electrolyte solvents selectedfrom the group consisting of N-methyl acetamide, acetonitrile,carbonates, sulfones, sulfolanes, aliphatic ethers, cyclic ethers,glymes, siloxanes, dioxolanes, N-alkyl pyrrolidones, substituted formsof the foregoing, and blends thereof; to which is added an appropriateionic electrolyte salt.

[0189] The electrolyte solvents of these liquid electrolytes arethemselves useful as plasticizers in semi-solid or gel polymerelectrolytes. Useful gel polymer electrolytes include, but are notlimited to, those comprising, in addition to one or more electrolytesolvents sufficient to provide the desired semi-solid or gel state, oneor more polymers. Examples of suitable polymers include, but are notlimited to those selected from the group consisting of polyethyleneoxides (PEO), polypropylene oxides, polyacrylonitriles, polysiloxanes,polyphosphazenes, polyimides, polyethers, sulfonated polyimides,perfluorinated membranes (NAFION™ resins), polydivinyl polyethyleneglycols, polyethylene glycol diacrylates, polyethylene glycoldimethacrylates, derivatives of the foregoing, copolymers of theforegoing, crosslinked and network structures of the foregoing, andblends of the foregoing; to which is added an appropriate ionicelectrolyte salt.

[0190] Solid polymer electrolytes useful in the present inventioninclude, but are not limited to, those comprising one or more polymersselected from the group consisting of: polyethers, polyethylene oxides(PEO), polypropylene oxides, polyimides, polyphosphazenes,polyacrylonitriles (PAN), polysiloxanes, polyether graftedpolysiloxanes, derivatives of the foregoing, copolymers of theforegoing, crosslinked and network structures of the foregoing, andblends of the foregoing; to which is added an appropriate ionicelectrolyte salt. The solid polymer electrolytes of this invention mayoptionally further comprise one or more electrolyte solvents, typicallyless than 20% by weight.

[0191] To improve the ionic conductivity and other electrochemicalproperties of the electrolyte element, the organic electrolyte typicallycomprises one or more ionic electrolyte salts. As used herein, liquidelectrolytes, gel polymer electrolytes, and solid polymer electrolytescomprise an ionic electrolyte salt.

[0192] Examples of ionic electrolyte salts for use in the presentinvention include, but are not limited to, MBr, MI, MClO₄, MAsF₆, MSCN,MSO₃CF₃, MSO₃CH₃, MBF₄, MB(Ph)₄,

[0193] Other electrolyte salts useful in the practice of this inventionare lithium polysulfides, lithium salts of organic ionic polysulfidesand those disclosed in U.S. Pat. No. 5,538,812 to Lee et al. Preferredionic electrolyte salts are LiI, LiSCN, LiSO₃CF₃ (lithium triflate) andLiN(SO₂CF₃)₂ (lithium imide).

[0194] Since the microporous pseudo-boehmite layer of this invention isusually impermeable to high molecular weight materials such as thepolymers typically used in gel polymer electrolytes and solid polymerelectrolytes, it is preferable to introduce the polymer component of theelectrolyte in a low molecular weight monomer or macromonomer form intopores of the pseudo-boehmite layer. Subsequently, the low molecularweight monomer or macromonomer may be cured into a polymer to providethe desired type of solid polymer or gel polymer electrolyte. Suitablemonomers or macromonomers include, but are not limited to, heat- orradiation-curable monomers or macromonomers. Examples include, but arenot limited to, divinyl ethers such as tetraethyleneglycol divinylether. To provide sensitivity to ultraviolet (UV) or visible radiationwhere the monomers or macromonomers do not absorb significantly, aconventional photosensitizer may be added to cause curing of themonomers or macromonomers into a polymeric material. For example, asmall amount, such as 0.2% by weight of the monomers or macromonomers,of a UV sensitizer may be added.

[0195] A particular advantage of the ultrafine pores and strongcapillary action of the pseudo-boehmite layer of the separator of thepresent invention is its excellent wetting by a broad variety ofelectrolytes and retention of these electrolytes in the pores.Accordingly, it is possible to incorporate liquid or tacky electrolytematerials into the nanoporous matrix of the pseudo-boehmite layerwithout having a significant excess of liquid or tacky material on thesurface of the separator. In one embodiment, the electrolyte material isheld below the outermost surface of the protective coatedpseudo-boehmite separator during the cell fabrication process. Forexample, this is useful in preventing the tacky surfaces of polymerelectrolytes from interfering with the fabrication processes of windingor layering a multiple layer construction of an electric currentproducing cell. For liquid organic electrolytes, no polymer is required,and the electrolyte composition may consist of only electrolyte solventsand ionic electrolyte salts

[0196] Electric Current Producing Cells and Methods of Preparing Same

[0197] The present invention provides an electric current producing cellcomprising a cathode and an anode and an electrolyte element interposedbetween the cathode and the anode, wherein the electrolyte elementcomprises (a) a separator comprising (i) at least one microporouspseudo-boehmite layer in contact with (ii) at least one protectivecoating layer, and (b) an electrolyte, preferably an organicelectrolyte, contained within pores of the separator, as describedherein for the separator and the electrolyte element, and for themethods of making the separator and electrolyte element of the presentinvention. The pseudo-boehmite layer of the separator typically has apore volume from 0.02 to 2.0 cm³/g, before the introduction of theelectrolyte, and has an average pore diameter from 1 nm to 300 nm, asdescribed herein for the microporous pseudo-boehmite layer of theseparator.

[0198] Although the electric current producing cell of the presentinvention may be utilized for a wide variety of primary and secondarybatteries known in the art, it is preferred to utilize these cells insecondary or rechargeable batteries where the many features of a freestanding or directly coated microporous pseudo-boehmite separator may beemployed to help control the chemistry of the active materials throughmany repeated discharge and charge cycles. Preferably, the batteries areof a prismatic configuration.

[0199] A wide variety of anode active materials may be utilized in theanodes for electric current producing cells of the present invention.Suitable anode active materials for the electric current producing cellsof the present invention include, but are not limited to, one or moremetals or metal alloys or a mixture of one or more metals and one ormore alloys, wherein said metals are selected from the Group IA and IIAmetals in the Periodic Table. Examples of suitable anode activematerials of the present invention include, but are not limited to,alkali-metal intercalated conductive polymers, such as lithium dopedpolyacetylenes, polyphenylenes, polypyrroles, and the like, andalkali-metal intercalated graphites and carbons. Anode active materialscomprising lithium are especially useful. Preferred anode activematerials are lithium metal, lithium-aluminum alloys, lithium-tinalloys, lithium-intercalated carbons, and lithium-intercalatedgraphites.

[0200] A wide variety of cathode active materials may be utilized in thecathodes for the electric producing cells of the present invention.Suitable cathodes for the cells of this invention include, but are notlimited to, cathodes comprising cathode active materials selected fromthe group consisting of: electroactive transition metal chalcogenides,electroactive conductive polymers, and electroactive sulfur-containingmaterials. Examples of suitable transition metal chalcogenides include,but are not limited to, the electroactive oxides, sulfides, andselenides of transition metals selected from the group consisting of Mn,V, Cr, Ti, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re,Os, and Ir. Preferred transition metal chalcogenides are electroactiveoxides of cobalt, manganese and vanadium. In one embodiment, the cathodeof the cell of this invention comprises an electroactive conductivepolymer. Examples of suitable conductive polymers include, but are notlimited to, electroactive and electronically conductive polymersselected from the group consisting of polypyrroles, polyphenylenes,polythiophenes, and polyacetylenes. Preferred conductive polymers arepolypyrroles and polyacetylenes.

[0201] Preferred cathode active materials are those comprisingelectroactive sulfur-containing materials. The term “electroactivesulfur-containing material,” as used herein, relates to cathode activematerials which comprise the element sulfur in any form, wherein theelectrochemical activity involves the breaking or forming ofsulfur-sulfur covalent bonds. The nature of the electroactivesulfur-containing materials useful in the cathodes of the cells of thisinvention may vary widely. The electroactive properties of elementalsulfur and of other sulfur-containing materials are well known in theart, and typically include the reversible formation of lithiated orlithium ion sulfides during the discharge or cathode reduction cycle ofthe battery.

[0202] In one embodiment, the electroactive sulfur-containing materialcomprises elemental sulfur.

[0203] In one embodiment, the electroactive sulfur-containing materialis organic, that is, it comprises both sulfur atoms and carbon atoms.

[0204] In one embodiment, the electroactive sulfur-containing materialis polymeric. In one embodiment, the sulfur-containing materialcomprises a sulfur-containing polymer comprising a polysulfide moiety,S_(m), selected from the group consisting of covalent —S_(m)— moieties,ionic —S_(m) ⁻ moieties, and ionic S_(m) ²⁻ moieties, wherein m is aninteger equal to or greater than 3. In one embodiment, m of thepolysulfide moiety, S_(m), of the sulfur-containing polymer is aninteger equal to or greater than 8. In one embodiment, the polysulfidemoiety, S_(m), is covalently bonded by one or both of its terminalsulfur atoms on a side group to the polymer backbone chain of thesulfur-containing polymer. In one embodiment, the polysulfide moiety,S_(m), comprises a covalent —S_(m)— moiety, which covalent —S_(m)—moiety is incorporated by covalent bonds to both of its terminal sulfuratoms into the polymer backbone chain of the sulfur-containing polymer.

[0205] Examples of electroactive sulfur-containing polymers include, butare not limited to, those comprising one or more carbon-sulfur polymersof general formulae (CS_(x))_(n) and (C₂S_(z))_(n). Compositionscomprising the general formula —(CS_(x))_(n)—, wherein x ranges from 1.2to 2.3, and n is an integer equal to or greater than 2, are described inU.S. Pat. No. 5,441,831 to Okamoto et al. Additional examples includethose wherein x ranges from greater than 2.3 to about 50, and n is equalto or greater than 2, as described in U.S. Pat. Nos. 5,601,947 and5,690,702 to Skotheim et al. Additional examples of electroactivesulfur-containing polymers include those compositions comprising thegeneral formula —(C₂S_(z))_(n)—, wherein z ranges from greater than 1 toabout 100, and n is equal to or greater than 2, as described in U.S.Pat. No. 5,529,860 and copending U.S. patent application Ser. No.08/602,323 to Skotheim et al. of the common assignee.

[0206] The preferred materials of general formulae (CS_(x))_(n) and(C₂S₂)_(n), in their oxidized state, comprise a polysulfide moiety ofthe formula, —S_(m)—, wherein m is an integer equal to or greater than3, or more preferably, wherein m is an integer from 3 to 10. In oneembodiment, m is an integer from 3 to 6. In one embodiment, m is aninteger from 3 to 8. In one embodiment, m is an integer from 6 to 10. Inone embodiment, m is an integer from 8 to 10. In one embodiment, thepolysulfide linkage comprises —S—S—S— (i.e., trisulfide). In oneembodiment, the polysulfide linkage comprises —S—S—S—S— (i.e.,tetrasulfide). In one embodiment, the polysulfide linkage comprises—S—S—S—S—S— (i.e., pentasulfide). In one embodiment, the polysulfidelinkage comprises —S—S—S—S—S—S— (i.e., hexasulfide). In one embodiment,the polysulfide linkage comprises —S—S—S—S—S—S—S— (i.e., heptasulfide).In one embodiment, the polysulfide linkage comprises —S—S—S—S—S—S—S—S—(i.e., octasulfide).

[0207] The backbone of electroactive sulfur-containing polymers maycomprise polysulfide —S_(m)— main chain linkages as well as covalentlybound —S_(m)— side groups. Owing to the presence of multiple linkedsulfur atoms, —S_(m)—, where m is an integer equal to or greater than 3,in these materials, they possess significantly higher energy densitiesthan corresponding materials containing the disulfide linkage, —S—S—,alone.

[0208] Other preferred electroactive sulfur-containing polymers arethose comprising carbocyclic repeat groups, as described in copendingU.S. patent application Ser. No. 08/995,112, to Gorkovenko et al. of thecommon assignee.

[0209] Other examples of electroactive sulfur-containing polymerscomprising a polysulfide moiety, S_(m), where m is an integer that isequal to or greater than 3, are those containing electron conductingpolymers and at least one polysulfurated chain forming a complex withthe polymer, as described in U.S. Pat. No. 4,664,991 to Perichaud etal.

[0210] Other examples of electroactive sulfur-containing polymersinclude organo-sulfur materials comprising disulfide linkages, althoughtheir low specific capacity compared to the corresponding materialscontaining polysulfide linkages makes it highly difficult to achieve thedesired high capacities in electric current producing cells. However,they may also be utilized in a blend in the cathode active layer withelemental sulfur and/or with sulfur-containing polymers comprising apolysulfide moiety in the solid composite cathodes of this invention andcontribute by their electrochemical properties, their known interactionwith lithium polysulfides and lithium sulfides generated during thecycling of the cells, and, optionally, their melting properties, toachieving the desired high capacities in the electric current producingcells of the present invention. Examples of these electroactivesulfur-containing materials comprising disulfide groups include thosedescribed in U.S. Pat. No. 4,739,018 to Armand et al.; U.S. Pat. Nos.4,833,048 and 4,917,974, both to DeJonghe et al.; U.S. Pat. Nos.5,162,175 and 5,516,598, both to Visco et al.; and U.S. Pat. No.5,324,599 to Oyama et al.

[0211] Other suitable examples of electroactive sulfur-containingmaterials include materials of general formula, C_(v)S, wherein v is anumerical value within the range of about 4 to about 50, as described inU.S. Pat. No. 4,143,214 to Chang et al. Other examples of electroactivesulfur-containing polymers are those which contain one or more polymercompounds having a plurality of carbon monosulfide units that maygenerally be written as (CS)_(w), wherein w is an integer of at least 5,as described in U.S. Pat. No. 4,152,491 to Chang et al.

[0212] Electroactive sulfur-containing polymers for the solid compositecathodes of the present invention typically have elemental compositionscontaining between about 50 weight percent and 98 weight percent sulfur.In one embodiment, the sulfur-containing polymer comprises greater than75 weight percent of sulfur, and, preferably, greater than 86 weight percent of sulfur, and, most preferably, greater than 90 weight percent ofsulfur.

[0213] In another embodiment of the electric current producing cell ofthe present invention, the electrolyte of the electrolyte element is anorganic electrolyte comprising one or more electrolytes selected fromthe group consisting of: liquid electrolytes, gel polymer electrolytesand solid polymer electrolytes.

[0214] A method for forming the electric current producing cell of thepresent invention comprises providing an anode and a cathode andinterposing an electrolyte element of the present invention, asdescribed herein, between the anode and the cathode. In one embodimentof the methods of forming the electric current producing cell, theelectrolyte of the electrolyte element is an organic electrolytecomprising one or more electrolytes selected from the group consistingof: liquid electrolytes, gel polymer electrolytes, and solid polymerelectrolytes.

[0215] The flexibility of the product designs and methods of forming theseparators and electrolyte elements of the present invention providesthe option of effectively incorporating electrolyte or the ionicelectrolyte salt of the electrolyte into the electric current producingcell at a later or final stage of fabricating materials into the cell.This may be advantageous when the ionic electrolyte salt is hygroscopicand difficult to coat as part of an electrolyte element and thendifficult to keep from absorbing water before fabrication and hermeticsealing of the cell in a dry room facility. This may also beadvantageous when the ionic electrolyte salt increases the viscosity andotherwise interferes with the wetting and penetration of a liquid orpolymer electrolyte into the separator and cathode layers during thefilling of the cell. In a preferred embodiment, the electrolyte iscontacted with the separator layer of the electrolyte element after theprocesses of winding or layering a multiple layer construction of anelectric current producing cell. For example, after the separator isenclosed between the anode and the cathode, there is a subsequent stepcomprising the imbibition of the electrolyte, for example, a solutioncomprising one or more ionic electrolyte salts and one or moreelectrolyte solvents, into the electrolyte element. In these multilayercell stacks, the excellent wetting and strong capillary action of theseparators of this invention are advantageous in promoting theimbibition and filling of the pores of the separator by the electrolyte,preferably a liquid organic electrolyte. In a most preferred embodiment,the electrolyte element that is enclosed between the anode and thecathode initially contains no ionic electrolyte salt, and the ionicelectrolyte salts required for the electrolyte element are provided by asubsequent step of imbibing a highly concentrated solution comprisingone or more ionic electrolyte salts and one or more electrolytesolvents. To achieve the desired final concentration of ionicelectrolyte salts in the organic electrolyte, the concentration of ionicelectrolyte salts in the imbibed highly concentrated solution will becorrespondingly much greater than this desired final concentration.

EXAMPLES

[0216] Several embodiments of the present invention are described in thefollowing examples, which are offered by way of illustration and not byway of limitation.

Comparative Example 1

[0217] A cathode was prepared by coating a mixture of 75 parts ofelemental sulfur (available from Aldrich Chemical Company, Milwaukee,Wis.), 20 parts of a conductive carbon pigment PRINTEX XE-2 (a trademarkfor a carbon pigment available from Degussa Corporation, Akron, Ohio),and 5 parts of PYROGRAF-III (a tradename for carbon filaments availablefrom Applied Sciences, Inc., Cedarville, Ohio) dispersed in isopropanolonto a 17 micron thick conductive carbon coated aluminum foil substrate(Product No. 60303 available from Rexam Graphics, South Hadley, Mass.).After drying and calendering, the coated cathode active layer thicknesswas about 12 microns. The anode was lithium foil of about 50 microns inthickness. The electrolyte was a 0.75 M solution of lithiumbis(trifluoromethyl)sulfonimide, (lithium imide available from 3MCorporation, St. Paul, Minn.) in a 50:50 volume ratio mixture of1,3-dioxolane and dimethoxyethane. The porous separator used was 16micron E25 SETELA (a trademark for a polyolefin separator available fromTonen Chemical Corporation, Tokyo, Japan, and also available from MobilChemical Company, Films Division, Pittsford, N.Y.).

[0218] The above components were combined into a layered structure ofcathode/separator/anode, which was wound and compressed, with the liquidelectrolyte filling the void areas of the separator and cathode to formprismatic cells with an electrode area of about 100 cm².Discharge-charge cycling on these cells was done at 0.5/0.3 mA/cm²,respectively, with discharge cutoff at a voltage of 1.3V and chargecutoff at 3V or 5 hour charge, whichever came first. Typical capacity ofthese cells was 90 mAh (specific capacity of 728 mAh/g of elementalsulfur in the cell) at the 5^(th) cycle with a total capacity fade ofabout 22% over the next 15 cycles.

Comparative Example 2

[0219] A microporous layer of pseudo-boehmite with binder present wasprepared according to the following procedure. A coating mixturecomprising 86 parts by weight (solid content) of DISPAL 11N7-12 (atrademark for boehmite sol available from CONDEA Vista Company, Houston,Tex.), 6 parts by weight (solid content) of AIRVOL 125 (a trademark forpolyvinyl alcohol polymer available from Air Products, Inc., Allentown,Pa.), 3 parts by weight of polyethylene oxide (900,000 MW from AldrichChemical Company, Milwaukee, Wis.) and 5 parts by weight polyethyleneoxide dimethylether, M-250, (Fluka Chemical Company, Ronkonkoma, N.Y.)in water was prepared. This coating mixture was coated directly on thecathode active layer from Comparative Example 1, using a gap coater sothat the dry pseudo-boehmite coating thickness would be about 12 micronsand followed by drying at 130° C. Prismatic cells were constructed as inComparative Example 1 except that the cathode and polyolefin separatorwere replaced by this pseudo-boehmite coated cathode. Discharge-chargecycling was performed on these cells at the same current density as inComparative Example 1. Capacity of these cells was 60 mAh (specificcapacity of 584 mAh/g of elemental sulfur in the cell) at the 5^(th)cycle with a total capacity fade of about 8% over the next 15 cycles.Fabrication of these prismatic cells was difficult because of thefragility of the pseudo-boehmite coating layer.

Example 1

[0220] A 5% by weight solution of a 3:2 ratio by weight of CD 9038 (atradename for ethoxylated bisphenol A diacrylate, available fromSartomer Inc., Exton, Pa.) and CN 984 (a tradename for a urethaneacrylate available from Sartomer Inc., Exton, Pa.) was prepared bydissolving these macromonomers in ethyl acetate. To this solution, 0.2%by weight (based on the total weight of acrylates) of ESCURE KTO (atradename for a photosensitizer available from Sartomer Inc., Exton,Pa.) was added. This solution was coated onto the pseudo-boehmite coatedcathode of Comparative Example 2 and dried to remove the solvent presentand to form the protective coating layer. The coating thickness of thedried protective coating layer comprising a polymer in the form ofmacromonomers on top of the microporous pseudo-boehmite layer was 4microns. The dried film was then cured by placing it on the conveyorbelt of a FUSION Model P300 UV exposure unit (available from FusionSystems Company, Torrance, Calif.) and exposing it to the UV lamps for30 seconds to form a cured protective coating layer comprising apolymer. Prismatic cells were constructed as in Comparative Example 2except that the pseudo-boehmite coated cathode was replaced by thisprotective coated pseudo-boehmite coated cathode. Discharge-chargecycling was performed on these cells at the same current density as inComparative Example 1. Capacity of these cells was 60 mAh (specificcapacity of 541 mAh/g of elemental sulfur in the cell) at the 5^(th)cycle with a total capacity fade of about 14% over the next 7 cycles.The flexibility and durability of the separator during the fabricationof the prismatic cells was significantly improved by the protectivecoating layer, and the cycling behavior of these cells was notsignificantly affected.

Example 2

[0221] Prismatic cells were prepared as in Example I except that theprotective coating solution contained, in addition to the macromonomersof Example 1, 5% by weight of CAB-O-SIL TS-530 (a trademark for a fumedsilica pigment available from Cabot Corporation, Tuscola, Ill.) whichwas dispersed in the solution by sonication. The thickness of thepigmented protective coating layer was about 4 microns. Discharge-chargecycling was performed on these cells at the same current density as inComparative Example 1. Typical capacity of these cells was 80 mAh(specific capacity of 708 mAh/g of elemental sulfur in the cell) at the5^(th) cycle with a total capacity fade of about 25% over the next 15cycles. The flexibility of the separator was improved by this topcoating, and the capacity of these cells was also improved. Fabricationof these prismatic cells was significantly improved over the prismaticcells comprising only a pseudo-boehmite coating layer of ComparativeExample 2.

Example 3

[0222] Prismatic cells were constructed as in Example 2 except that thecathode area was enlarged to 347 cm² and the electrolyte was a 1.4 Msolution of lithium imide in a 30:40 ratio by volume mixture of1,3-dioxolane and dimethoxyethane. Discharge-charge cycling wasperformed on these cells at the same current density as in ComparativeExample 1. Typical specific capacity of the cells was 729 mAh/g ofelemental sulfur in the cell at the 3^(rd) cycle with a total capacityfade of 3% over the next 20 cycles. The flexibility and toughness of theprotective coated separator permitted the fabrication of the largercells. Attempts to construct prismatic cells of 347 cm² according toComparative Example 2 were completely unsuccessful, due to the fragilityof the pseudo-boehmite layer without a protective coating.

Comparative Example 3

[0223] Prismatic cells were constructed as in Comparative Example 1except that the cathode area was enlarged to 347 cm², and theelectrolyte was that used in Example 3. Discharge-charge cycling wasperformed on these cells at the same current density as in ComparativeExample 1. Typical specific capacity of the cells was 963 mAh/g ofelemental sulfur in the cell at the 3^(rd) cycle with a total capacityfade of 14% over the next 20 cycles.

Example 4

[0224] Prismatic cells were constructed as in Example 3 except that thecathode area of each cell was 500 cm². Discharge-charge cycling wasperformed on these cells at the same current density as in ComparativeExample 1. The specific capacity of the cells were 850 mAh/g ofelemental sulfur in the cell at the 5^(th) cycle with a total capacityfade of 17% over the next 80 cycles. After 100 cycles, the averagecapacity of these cells was 77% of the specific capacity at the ₅thcycle.

Comparative Example 4

[0225] Prismatic cells were constructed as in Comparative Example 3except that the cathode area was 500 cm². Discharge-charge cycling wasperformed on these cells at the same current density as in ComparativeExample 1. The specific capacity of the cells were 812 mAh/g ofelemental sulfur in the cell at the 5th cycle with a total capacity fadeof 13% over the next 80 cycles.

Example 5

[0226] Prismatic cells were constructed as in Example 2 except that thecathode area was enlarged to 1000 cm². Discharge-charge cycling wasperformed on these cells at the same current density as in ComparativeExample 1. Typical capacity of the cells was 836 mAh (specific capacityof the cells was 669 mAh/g of elemental sulfur in the cell) at the5^(th) cycle, and at the 201^(st) cycle, the total capacity was 62% ofthe capacity at the 5^(th) cycle.

Example 6

[0227] Prismatic cells were prepared as in Example 2, except that thecathode area was enlarged to 800 cm², and after the protective coatinglayer comprising a polymer was cured, a second pseudo-boehmite layer of6 micron thickness was coated on top to form a separator comprisingthree layers: a first pseudo-boehmite layer, an intermediate protectivecoating layer, and a second pseudo-boehmite layer. The electrolyte was a1.4 M solution of lithium imide in a 30:40 by volume mixture of1,3-dioxolane and dimethoxyethane. Discharge-charge on this cell wasperformed at the current density of 0.44/0.25 mA/cm², respectively.Typical capacity of this cell was 911 mAh at the 5^(th) cycle with acapacity fading of about 0.9% over the next 30 cycles.

Example 7

[0228] A 3% solution of poly(butyl methacrylate), M.W. 337,000,(available from Aldrich Chemical Company, Milwaukee, Wis.) was preparedin ethyl acetate. The cathode active layer of Comparative Example 1 wascoated with the poly (butyl methacrylate) solution to yield a protectivecoating layer of about 1 micron thickness after drying. Upon thisprotective coating layer was coated a pseudo-boehmite layer of about 12micron thickness, as described in Comparative Example 2. After dryingthe pseudo-boehmite layer, a third layer protective polymer coatinglayer, as described in Example 2, was coated on top of thepseudo-boehmite layer with a coating layer thickness of about 4 micron.This separator coated on top of the cathode active layer comprised threelayers: (1) a first protective coating layer, (2) an intermediatepseudo-boehmite layer, and (3) a second protective coating layer.

[0229] Vial cells were constructed as in Comparative Example 2.Discharge-charge cycling on these cells was performed at the samecurrent density as in Comparative Example 1. Typical specific capacityof these cells was 600 to 670 mAh/g of elemental sulfur in the cell atthe 5^(th) cycle and 635 to 700 mAh/g of elemental sulfur in the cell atthe 50^(th) cycle. The fading rate of capacity calculated from the5^(th) cycle was about 0.5% per cycle over the next 100 cycles.

Example 8

[0230] The cathode active layer of Comparative Example 1 was coated witha pseudo-boehmite separator layer of about 6 micron thickness, as inComparative Example 2. This separator layer was coated with the poly(butyl methacrylate) solution of Example 7 to yield a coating of about 4micron thickness after drying. Upon this coating was next coated asecond pseudo-boehmite layer of about 6 micron thickness. This separatorcoated on the cathode comprised three layers: (1) a firstpseudo-boehmite layer, (2) an intermediate protective coating layercomprising a polymer layer, and (3) a second pseudo-boehmite layer.

[0231] Vial cells were constructed as in Example 7 and discharge-chargecycling of these cells was performed at the same current density as inComparative Example 1. Typical specific capacity of these cells was 680to 715 mAh/g of elemental sulfur in the cell at the 5^(th) cycle, and650 to 720 mAh/g of elemental sulfur in the cell at the 50^(th) cycle.The fading rate of capacity calculated from the 5^(th) cycle was about0.2% per cycle over the next 100 cycles.

Comparative Example 5

[0232] A cathode was prepared by coating a mixture of 65 parts ofelemental sulfur, 15 parts of a conductive carbon pigment PRINTEX XE-2,15 parts of a graphite pigment (available from Fluka Chemical Company,Ronkonkoma, N.Y.), and 5 parts of fumed silica CAB-O-SIL EH-5 (atradename for silica pigment available from Cabot Corporation, Tuscola,Ill.) dispersed in isopropanol onto a 17 micron thick conductive carboncoated aluminum coated PET substrate (available from Rexam Graphics,South Hadley, Mass.). After drying and calendering, the coated cathodeactive layer thickness was about 15-18 microns. The anode was lithiumfoil of about 50 microns in thickness. The electrolyte was a 1.4 Msolution of lithium bis(trifluoromethyl)sulfonimide in a 30:40 volumeratio mixture of 1,3-dioxolane and dimethoxyethane. The porouspolyolefin separator used was 16 micron E25 SETELA.

[0233] The above components were combined into a layered structure ofcathodelseparator/anode, which was wound and compressed, with the liquidelectrolyte filling the void areas of the separator and cathode to formprismatic cells with an electrode area of about 800 cm².Discharge-charge cycling on these cells was done at 0.44/0.31 mA/cm²,respectively, with discharge cutoff at a voltage of 1.5V and chargecutoff at 2.8V or 120% overcharge, whichever came first. Typicalcapacity of these cells was 700-800 mAh (specific capacity of 800-900mAh/g of elemental sulfur in the cell) at the 5^(th) cycle with a totalcapacity fade of about 2.5% over the next 15 cycles.

Example 9

[0234] The cathode active layer of Comparative Example 5 was coated witha 15% by weight solution of a 1:1 mixture of Hycar 1571 and Hycar 1578x1(tradenames for acrylonitrile-butadiene andacrylonitrile-butadiene-styrene latex emulsions, respectively, availablefrom B.F. Goodrich Specialty Chemicals, Cleveland, Ohio) to yield afirst protective coating layer of about 2 micron thickness after drying.Upon this protective coating layer was coated a pseudo-boehmite layer ofabout 10 micron thickness, as described in Comparative Example 2. Afterdrying the pseudo-boehmite layer, a third layer, a second protectivepolymer coating layer, as described in Example 2, was coated on top ofthe pseudo-boehmite layer with a coating layer thickness of about 3microns. The separator coated on top of the cathode active layer thuscomprised three layers: (1) a first protective coating layer, (2) anintermediate pseudo-boehmite layer, and (3) a second protective coatinglayer.

[0235] Prismatic cells were constructed as in Comparative Example 5,except that the cathode and polyolefin separator were replaced by thisseparator coated cathode. Discharge-charge cycling on these cells wasperformed at the same current density as in Comparative to Example 5.Typical specific capacity of these cells was approximately 670 mAh/g ofelemental sulfur in the cell at the 10^(th) cycle. The total capacityfade over the next 15 cycles was 7.7%.

Example 10

[0236] The pseudo-boehmite coated cathode of Comparative Example 2 wascoated with a 15%, by weight, solution of a 1:1 mixture of Hycar 1571and Hycar 1578x1 to form a first protective coating layer of about 2micron thickness after drying to remove the solvent present. The polymersolution of Example 1 was coated on this latex polymer coatedpseudo-boehmite layer and dried. The coating thickness of the seconddried protective coating layer comprising a polymer in the form ofmacromonomers on top of the microporous pseudo-boehmite layer was 4microns. The dried film was then cured using UV lamps as described inExample 1 to form a cured second protective coating layer comprising apolymer. This separator coated on top of the cathode active layercomprised three layers: (1) a pseudo-boehmite layer, (2) a firstprotective coating layer, and (3) a second protective coating layer.

[0237] Prismatic cells were constructed as in Comparative Example 2except that the pseudo-boehmite coated cathode was replaced by thisprotective coated pseudo-boehmite coated cathode. Discharge-chargecycling was performed on these cells at the same current density as inComparative Example 5. Typical specific capacity of these cells wasapproximately 550 mAh/g of elemental sulfur in the cell at the 5^(th)cycle.

Example 11

[0238] The pseudo-boehmite coated cathode of Comparative Example 2 wascoated with a 15%, by weight, solution of a 1:1 mixture of Hycar 1571and Hycar 1578x1 to form a first protective coating layer of about 2micron thickness after drying to remove the solvent present. Upon thiscoating was coated a second pseudo-boehmite layer of approximately 6micron thickness. The polymer solution of Example 1 was coated on thissecond pseudo-boehmite layer, dried and cured. The coating thickness ofthe second dried protective coating layer comprising a polymer in theform of macromonomers on top of the microporous pseudo-boehmite layerwas 4 microns. This separator coated on top of the cathode active layercomprised four layers: (1) a first pseudo-boehmite layer, (2) a firstprotective coating layer, (3) a second pseudo-boehmite layer, and (4) asecond protective coating layer.

[0239] Prismatic cells were constructed as in Comparative Example 2except that the pseudo-boehmite coated cathode was replaced by thisprotective coated pseudo-boehmite coated cathode. Discharge-chargecycling was performed on these cells at the same current density as inComparative Example 5. Typical specific capacity of these cells wasapproximately 620 mAh/g of elemental sulfur in the cell at the 5^(th)cycle.

[0240] While the invention has been described in detail and withreference to specific and general embodiments thereof, it will beapparent to one skilled in the art that various changes andmodifications can be made therein without departing from the spirit andscope thereof.

1. A separator for use in an electric current producing cell, whereinsaid cell comprises a cathode having a cathode active layer, an anode,and an electrolyte element interposed between said cathode and saidanode, wherein said electrolyte element comprises said separator and anelectrolyte; and said separator comprises at least one microporouspseudo-boehmite layer wherein said separator is in contact with at leastone protective coating layer; and wherein at least one of said at leastone protective coating layers is on the anode-facing side of saidseparator opposite from said cathode active layer of said cell.
 2. Theseparator of claim 1 , wherein at least one of said protective coatinglayers on said anode-facing side comprises a polymer.
 3. The separatorof claim 2 , wherein said protective coating layer comprising a polymeris a single ion conducting layer.
 4. The separator of claim 2 , whereinsaid protective coating layer comprising a polymer comprises aconductive polymer selected from the group consisting ofpoly(p-phenylene), polyacetylene, poly(phenylenevinylene), polyazulene,poly(perinaphthalene), polyacenes, and poly(naphthalene-2,6-diyl). 5.The separator of claim 1 , wherein at least one of said protectivecoating layers on said anode-facing side is a single ion conductivelayer.
 6. The separator of claim 1 , wherein at least one of saidprotective coating layers on said anode-facing side comprises a singleion conducting glass conductive to lithium ions.
 7. The separator ofclaim 6 , wherein said single ion conducting glass is selected from thegroup consisting of lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumtitanium oxides, lithium lanthanum oxides, lithium silicosulfides,lithium borosulfides, lithium aluminosulfides, lithium germanosulfides,and lithium phosphosulfides, and combinations thereof.
 8. The separatorof claim 1 , wherein at least one of said protective coating layers onsaid anode-facing side comprises a lithium phosphorus oxynitride.
 9. Theseparator of claim 2 , wherein said protective coating layer has athickness of from 0.2 to 20 microns.
 10. The separator of claim 2 ,wherein said protective coating layer has a thickness of from 0.5 to 5microns.
 11. The separator of claim 6 , wherein said protective coatinglayer has a thickness of from 5 n to 5 microns.
 12. The separator ofclaim 1 , wherein said separator is in contact with a first and a secondprotective coating layer, wherein said first protective coating layer isin contact with said pseudo-boehmite layer on the side of said separatoropposite from said cathode active layer, and said second protectivecoating layer is in contact with said first protective coating layer onthe side opposite from said pseudo-boehmite layer.
 13. The separator ofclaim 12 , wherein said second protective coating layer comprises asingle ion conducting glass conductive to lithium ions.
 14. Theseparator of claim 13 , wherein the combined thickness of said twoprotective coating layers is from 10 nm to 20 microns.
 15. The separatorof claim 2 , wherein said protective coating layer comprises one or moremoieties formed by the polymerization of one or more monomers ormacromonomers selected from the group consisting of monomers ormacromonomers having the formula: R¹(R²O)_(n)—R³ wherein: R¹ is the sameor different at each occurrence and is selected from the groupconsisting of CH₂═CH(C-O)—O—, CH₂═C(CH₃)(C═O)O—, CH₂═CH—,

CH₂=CH—O—; R² is the same or different at each occurrence and isselected from the group consisting of —CH₂—CH₂—, —CH(CH₃)—CH₂—,—CH₂—CH₂—CH₂—, —CH(C₂H₅)—CH₂—, —CH₂—CH₂—CH₂—CH₂—; R³ is the same ordifferent at each occurrence and is selected from the group consistingof cyano, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl,2-ethylhexyl, decyl, dodecyl, phenyl, butylphenyl, octylphenyl,nonylphenyl, R¹, —X—(OR²)_(m)—R¹, —Y[(OR²)_(o)—R¹]₂, —Z[(OR²)_(p)—R¹]₃;X is a divalent radical selected from the group consisting of

Y is a trivalent radical selected from the group consisting of

Z is a tetravalent radical selected from the group consisting of

m is an integer ranging from 0 to 100; n is an integer ranging from 0 to100; o is an integer ranging from 0 to 100; and, p is an integer rangingfrom 0 to
 100. 16. The separator of claim 2 , wherein said protectivecoating layer comprises one or more moieties formed by polymerization ofone or more acrylates selected from the group consisting of polyethyleneglycol diacrylates, polypropylene glycol diacrylates, ethoxylatedneopentyl glycol diacrylates, ethoxylated bisphenol A diacrylates,ethoxylated aliphatic urethane acrylates, ethoxylated alkylphenolacrylates, and alkyl acrylates.
 17. The separator of claim 2 , whereinsaid protective coating layer comprises a polymer selected from thegroup consisting of polyacrylates, polymethacrylates, polyolefins,polyurethanes, polyvinyl ethers, polyvinyl pyrrolidones,acrylonitrile-butadiene rubber, styrene-butadiene rubber,acrylonitrile-butadiene-styrene, sulfonatedstyrene/ethylene-butylene/styrene triblock polymers, and mixturesthereof.
 18. A method of making a separator for use in an electriccurrent producing cell, wherein said cell comprises a cathode having acathode active layer, an anode, and an electrolyte element interposedbetween said cathode and said anode, wherein said electrolyte elementcomprises said separator and an electrolyte; and said separatorcomprises at least one microporous pseudo-boehmite layer, wherein saidseparator is in contact with at least one protective coating layer; andwherein at least one of said protective coating layers is on theanode-facing side of said separator opposite from said cathode activelayer of said cell; wherein said method comprises the steps of: (a)coating onto a substrate a first liquid mixture, A, comprising aboehmite sol, to form a first coating layer; (b) drying the firstcoating layer formed in step (a) to form said separator comprising amicroporous pseudo-boehmite layer; (c) coating onto said separator layerformed in step (b) a mixture of a protective coating material to form asecond coating layer; (d) removing any volatile liquids of said secondcoating layer formed in step (c) to form a first protective coatinglayer on said anode-facing side of said separator.
 19. The method ofclaim 18 , wherein said mixture of step (c) comprises one or morepolymers, monomers, or macromonomers, and wherein step (d) comprises astep of drying the second coating layer formed in step (c) to form saidfirst protective coating layer, wherein said first protective coatinglayer comprises a polymer.
 20. The method of claim 18 , wherein saidfirst protective coating layer is formed by a physical depositionprocess or a chemical vapor deposition process in steps (c) and (d). 21.The method of claim 20 , wherein said first protective coating layercomprises a single ion conducting glass conductive to lithium ions. 22.The method of claim 21 , wherein said single ion conducting glass isselected from the group consisting of lithium silicates, lithiumborates, lithium aluminates, lithium phosphates, lithium phosphorusoxynitrides, lithium titanium oxides, lithium lanthanum oxides, lithiumsilicosulfides, lithium borosulfides, lithium aluminosulfides, lithiumgermanosulfides, and lithium phosphosulfides.
 23. The method of claim 20, wherein said first protective coating layer comprises a lithiumphosphorus oxynitride.
 24. The method of claim 20 , wherein said firstprotective coating layer comprises a conductive polymer selected fromthe group consisting of poly(p-phenylene), polyacetylene,poly(phenylenevinylene), polyazulene, poly(perinaphthalene), polyacenes,and poly(naphthalene-2,6-diyl).
 25. The method of claim 19 , whereinsaid first protective coating layer has a thickness of from 0.2 to 20microns.
 26. The method of claim 19 , wherein said first protectivecoating layer has a thickness of from 0.5 to 5 microns.
 27. The methodof claim 20 , wherein said first protective coating layer has athickness of from 5 nm to 5 microns.
 28. The method of claim 18 ,wherein after step (d) the method comprises a step (e) of coating ontothe layer formed in step (d) a second protective coating layer.
 29. Themethod of claim 28 , wherein step (e) comprises the steps of: (i)coating onto said second coating layer formed in step (d) a mixture of aprotective coating material to form a third coating layer; (ii) removingany volatile liquids of said third coating layer formed in step (i) toform a second protective coating layer on said anode-facing side of saidseparator.
 30. The method of claim 28 , wherein said second protectivelayer is formed in step (e) by a physical deposition process or achemical vapor deposition process.
 31. The method of claim 19 , wherein,subsequent to step (d), there is a step (e) of curing said protectivecoating layer to form a cured protective coating layer by use of anenergy source.
 32. The method of claim 31 , wherein said curing isperformed using an energy source selected from the group consisting ofheat, ultraviolet light, visible light, infrared radiation, and electronbeam radiation.
 33. The method of claim 19 , wherein at least one ofsaid one or more polymers, monomers and macromonomers has a molecularweight which is too large for impregnation into the pores of saidmicroporous pseudo-boehmite layer.
 34. The method of claim 19 , whereinat least one of said one or more monomers and macromonomers for use informing said protective coating layer is selected from the groupconsisting of monomers or macromonomers having the formula:R¹(R²O)_(n)—R³ wherein: R¹ is the same or different at each occurrenceand is selected from the group consisting of CH₂═CH(C═O)—O—,CH₂═C(CH₃)(C═O)O—, CH₂═CH—,

CH₂═CH—O—; R² is the same or different at each occurrence and isselected from the group consisting of —CH₂—CH₂—, —CH(CH₃)—CH₂—,—CH₂—CH₂—CH₂—, —CH(C₂H₅)—CH₂—, —CH₂—CH₂—CH₂—CH₂—; R³ is the same ordifferent at each occurrence and is selected from the group consistingof cyano, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl,2-ethylhexyl, decyl, dodecyl, phenyl, butylphenyl, octylphenyl,nonylphenyl, R¹, —X—(OR²)_(m)—R¹, —Y[(OR²)_(o)—R¹]₂, —Z[(OR²)_(p)—R¹]₃;X is a divalent radical selected from the group consisting of

Y is a trivalent radical selected from the group consisting of

Z is a tetravalent radical selected from the group consisting of

m is an integer ranging from 0 to 100; n is an integer ranging from 0 to100; o is an integer ranging from 0 to 100; and, p is an integer rangingfrom 0 to
 100. 35. The method of claim 19 , wherein at least one of saidone or more monomers or macromonomers is an acrylate selected from thegroup consisting of polyethylene glycol diacrylates, polypropyleneglycol diacrylates, ethoxylated neopentyl glycol diacrylates,ethoxylated bisphenol A diacrylates, ethoxylated aliphatic urethaneacrylates, ethoxylated alkylphenol acrylates, and alkyl acrylates. 36.The method of claim 19 , wherein said polymer of said first protectivecoating layer has a molecular weight greater than 10,000.
 37. The methodof claim 19 , wherein said polymer of said first protective coatinglayer has a molecular weight greater than 50,000.
 38. The method ofclaim 19 , wherein said mixture of step (c) comprises a polymer.
 39. Themethod of claim 38 , wherein said polymer is selected from the groupconsisting of polyacrylates, polymethacrylates, polyolefins,polyurethanes, polyvinyl ethers, polyvinyl pyrrolidones,acrylonitrile-butadiene rubber, styrene-butadiene rubber,acrylonitrile-butadiene-styrene, sulfonatedstyrene/ethylene-butylene/styrene triblock polymers, and mixturesthereof.
 40. A method for making an electrolyte element for use in anelectric current producing cell, wherein said electrolyte elementcomprises a separator comprising at least one microporouspseudo-boehmite layer, wherein said separator is in contact with atleast one protective coating layer; and wherein at least one of saidprotective coating layers is on the anode-facing side of said separatoropposite from a cathode active layer in said cell; wherein said methodcomprises the steps of: (a) coating onto a substrate a first liquidmixture, A, comprising a boehmite sol, to form a first coating layer;(b) drying the first coating layer formed in step (a) to form saidseparator comprising a microporous pseudo-boehmite layer; (c) coatingonto said separator layer formed in step (b) a mixture of a protectivecoating material to form a second coating layer; (d) removing anyvolatile liquids of said second coating layer formed in step (c) to forma first protective coating layer on said anode-facing side; and (e)contacting a surface of the structure formed in step (d) with anelectrolyte, thereby causing infusion of said electrolyte into the poresof said separator.
 41. The method of claim 40 , wherein said mixture ofstep (c) comprises one or more polymers, monomers, or macromonomers, andwherein step (d) comprises a step of drying the second coating layerformed in step (c) to form said first protective coating layer, whereinsaid first protective coating layer comprises a polymer.
 42. The methodof claim 40 , wherein said first protective coating layer is formed by aphysical deposition process or a chemical vapor deposition process insteps (c) and (d).
 43. The method of claim 40 , wherein said methodcomprises, subsequent to step (d) and before step (e), a step ofdelaminating said separator layer from said substrate.
 44. The method ofclaim 40 , wherein at least one outermost surface of said substratecomprises a cathode active layer and said first liquid mixture of step(a) is coated onto said cathode active layer.
 45. The method of claim 40, wherein said electrolyte comprises one or more materials selected fromthe group consisting of liquid electrolytes, gel polymer electrolytes,and solid polymer electrolytes.
 46. The method of claim 40 , whereinsaid electrolyte is an organic electrolyte.
 47. The method of claim 40 ,wherein said electrolyte is an aqueous electrolyte.
 48. An electriccurrent producing cell comprising a cathode, an anode, and anelectrolyte element interposed between said cathode and said anode,wherein said electrolyte element comprises; (a) a separator; and, (b) anelectrolyte; wherein said separator comprises at least one microporouspseudo-boehmite layer, wherein said separator is in contact with atleast one protective coating layer; and wherein at least one of said atleast one protective coating layers is on the anode-facing side of saidseparator opposite from said cathode active layer of said cell, and saidelectrolyte is contained within the pores of said separator.
 49. Thecell of claim 48 , wherein said cell is a secondary electric currentproducing cell.
 50. The cell of claim 48 , wherein said cell is aprimary electric current producing cell.
 51. An electric currentproducing cell comprising a cathode, an anode, and an electrolyteelement interposed between said cathode and said anode, wherein saidelectrolyte element comprises: (a) a separator; and, (b) an organicelectrolyte; wherein, said separator comprises: (i) a microporouspseudo-boehmite layer, in contact with (ii) a protective coating layercomprising a polymer; and, wherein said organic electrolyte is containedwithin the pores of said separator.
 52. The cell of claim 51 , whereinsaid protective coating layer is on the anode-facing side of saidseparator opposite from said cathode.
 53. A method of forming anelectric current producing cell, said method comprising the steps of:(a) providing an anode; (b) providing a cathode; and, (c) interposing anelectrolyte element between said anode and said cathode, wherein saidelectrolyte element comprises (i) a separator according to claim 1 ; and(ii) an electrolyte within the pores of said separator.
 54. The methodof claim 53 , wherein said electrolyte of said electrolyte elementcomprises one or more electrolytes selected from the group consisting ofliquid electrolytes, gel polymer electrolytes, and solid polymerelectrolytes.